r"""
Boolean Polynomials

Elements of the quotient ring

.. MATH::

    \GF{2}[x_1,...,x_n]/<x_1^2+x_1,...,x_n^2+x_n>.

are called boolean polynomials. Boolean polynomials arise naturally in
cryptography, coding theory, formal logic, chip design and other
areas. This implementation is a thin wrapper around the PolyBoRi
library by Michael Brickenstein and Alexander Dreyer.

"Boolean polynomials can be modelled in a rather simple way, with
both coefficients and degree per variable lying in
``{0, 1}``. The ring of Boolean polynomials is, however,
not a polynomial ring, but rather the quotient ring of the
polynomial ring over the field with two elements modulo the field
equations `x^2=x` for each variable `x`. Therefore,
the usual polynomial data structures seem not to be appropriate for
fast Groebner basis computations. We introduce a specialised data
structure for Boolean polynomials based on zero-suppressed binary
decision diagrams (ZDDs), which is capable of handling these
polynomials more efficiently with respect to memory consumption and
also computational speed. Furthermore, we concentrate on high-level
algorithmic aspects, taking into account the new data structures as
well as structural properties of Boolean polynomials." - [BD2007]_

For details on the internal representation of polynomials see

    http://polybori.sourceforge.net/zdd.html

AUTHORS:

- Michael Brickenstein: PolyBoRi author

- Alexander Dreyer: PolyBoRi author

- Burcin Erocal <burcin@erocal.org>: main Sage wrapper author

- Martin Albrecht <malb@informatik.uni-bremen.de>: some
  contributions to the Sage wrapper

- Simon King <simon.king@uni-jena.de>:
  Adopt the new coercion model. Fix conversion from univariate
  polynomial rings. Pickling of :class:`BooleanMonomialMonoid`
  (via :class:`~sage.structure.unique_representation.UniqueRepresentation`)
  and :class:`BooleanMonomial`.

- Charles Bouillaguet <charles.bouillaguet@gmail.com>: minor changes
  to improve compatibility with MPolynomial and make the variety()
  function work on ideals of BooleanPolynomial's.


EXAMPLES:

Consider the ideal


.. MATH::

    <ab + cd + 1, ace + de, abe + ce, bc + cde + 1>.

First, we compute the lexicographical Groebner basis in the polynomial
ring

.. MATH::

    R = \GF{2}[a,b,c,d,e].

::

    sage: P.<a,b,c,d,e> = PolynomialRing(GF(2), 5, order='lex')
    sage: I1 = ideal([a*b + c*d + 1, a*c*e + d*e, a*b*e + c*e, b*c + c*d*e + 1])
    sage: for f in I1.groebner_basis():
    ....:   f
    a + c^2*d + c + d^2*e
    b*c + d^3*e^2 + d^3*e + d^2*e^2 + d*e + e + 1
    b*e + d*e^2 + d*e + e
    c*e + d^3*e^2 + d^3*e + d^2*e^2 + d*e
    d^4*e^2 + d^4*e + d^3*e + d^2*e^2 + d^2*e + d*e + e

If one wants to solve this system over the algebraic closure of
`\GF{2}` then this Groebner basis was the one to consider. If one
wants solutions over `\GF{2}` only then one adds the field polynomials
to the ideal to force the solutions in `\GF{2}`.

::

    sage: J = I1 + sage.rings.ideal.FieldIdeal(P)
    sage: for f in J.groebner_basis():
    ....:   f
    a + d + 1
    b + 1
    c + 1
    d^2 + d
    e

So the solutions over `\GF{2}` are `\{e=0, d=1, c=1, b=1, a=0\}` and
`\{e=0, d=0, c=1, b=1, a=1\}`.

We can express the restriction to `\GF{2}` by considering the quotient
ring. If `I` is an ideal in `\Bold{F}[x_1, ..., x_n]` then the
ideals in the quotient ring `\Bold{F}[x_1, ..., x_n]/I` are in
one-to-one correspondence with the ideals of `\Bold{F}[x_0, ...,
x_n]` containing `I` (that is, the ideals `J` satisfying `I \subset J
\subset P`).

::

    sage: Q = P.quotient( sage.rings.ideal.FieldIdeal(P) )
    sage: I2 = ideal([Q(f) for f in I1.gens()])
    sage: for f in I2.groebner_basis():
    ....:     f
    abar + dbar + 1
    bbar + 1
    cbar + 1
    ebar

This quotient ring is exactly what PolyBoRi handles well::

    sage: B.<a,b,c,d,e> = BooleanPolynomialRing(5, order='lex')
    sage: I2 = ideal([B(f) for f in I1.gens()])
    sage: for f in I2.groebner_basis():
    ....:   f
    a + d + 1
    b + 1
    c + 1
    e

Note that ``d^2 + d`` is not representable in ``B == Q``. Also note, that
PolyBoRi cannot play out its strength in such small examples,
i.e. working in the polynomial ring might be faster for small examples
like this.

Implementation specific notes
-----------------------------

PolyBoRi comes with a Python wrapper. However this wrapper does not
match Sage's style and is written using Boost. Thus Sage's wrapper is
a reimplementation of Python bindings to PolyBoRi's C++ library.  This
interface is written in Cython like all of Sage's C/C++ library
interfaces. An interface in PolyBoRi style is also provided which is
effectively a reimplementation of the official Boost wrapper in
Cython. This means that some functionality of the official wrapper
might be missing from this wrapper and this wrapper might have bugs
not present in the official Python interface.

Access to the original PolyBoRi interface
-----------------------------------------

The re-implementation PolyBoRi's native wrapper is available to the
user too::

    sage: from brial import *
    sage: declare_ring([Block('x',2),Block('y',3)],globals())
    Boolean PolynomialRing in x0, x1, y0, y1, y2
    sage: r
    Boolean PolynomialRing in x0, x1, y0, y1, y2

::

    sage: [Variable(i, r) for i in range(r.ngens())]
    [x(0), x(1), y(0), y(1), y(2)]

For details on this interface see:

  http://polybori.sourceforge.net/doc/tutorial/tutorial.html.

Also, the interface provides functions for compatibility with Sage
accepting convenient Sage data types which are slower than their
native PolyBoRi counterparts. For instance, sets of points can be
represented as tuples of tuples (Sage) or as ``BooleSet`` (PolyBoRi)
and naturally the second option is faster.
"""

from cpython.object cimport Py_EQ, Py_NE
from cython.operator cimport dereference as deref
from cysignals.memory cimport sig_malloc, sig_free
from cysignals.signals cimport sig_on, sig_off
from sage.ext.cplusplus cimport ccrepr

import operator

from sage.cpython.string cimport str_to_bytes, char_to_str

from sage.misc.cachefunc import cached_method

from sage.misc.randstate import current_randstate
from sage.arith.long cimport pyobject_to_long
import sage.misc.weak_dict
from sage.rings.integer import Integer
from sage.rings.finite_rings.finite_field_constructor import FiniteField as GF

from sage.rings.polynomial.polynomial_element cimport Polynomial
from sage.rings.polynomial.multi_polynomial_ideal import MPolynomialIdeal
from sage.rings.polynomial.term_order import TermOrder
from sage.rings.polynomial.polynomial_ring import PolynomialRing_general

from sage.rings.ideal import FieldIdeal

from sage.structure.coerce cimport coercion_model
from sage.structure.element cimport Element

from sage.structure.parent cimport Parent
from sage.structure.sequence import Sequence
from sage.structure.element import coerce_binop
from sage.structure.unique_representation import UniqueRepresentation
from sage.structure.richcmp cimport richcmp, richcmp_not_equal

from sage.categories.action cimport Action

from sage.monoids.monoid import Monoid_class

from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
from sage.interfaces.all import singular as singular_default
from sage.interfaces.singular import SingularElement

order_dict = {"lp": pblp,
              "dlex": pbdlex,
              "dp_asc": pbdp_asc,
              "dp": pbdp,
              "block_dlex": pbblock_dlex,
              "block_dp_asc": pbblock_dp_asc,
              "block_dp": pbblock_dp}


inv_order_dict = {pblp: "lex",
                  pbdlex: "deglex",
                  pbdp_asc: "degneglex",
                  pbdp: "degrevlex"}


order_mapping = {'lp': pblp,
                 'lex': pblp,
                 'Dp': pbdlex,
                 'deglex': pbdlex,
                 'dlex': pbdlex,
                 'dp_asc': pbdp_asc,
                 'degneglex': pbdp_asc,
                 'dp': pbdp,
                 'degrevlex': pbdp}


lp = int(pblp)
dlex = int(pbdlex)
dp = int(pbdp)
dp_asc = int(pbdp_asc)
block_dlex = int(pbblock_dlex)
block_dp_asc = int(pbblock_dp_asc)

rings = sage.misc.weak_dict.WeakValueDictionary()


cdef class BooleanPolynomialRing(MPolynomialRing_base):
    """
    Construct a boolean polynomial ring with the following parameters:

    INPUT:

    -  ``n`` - number of variables (an integer > 1)

    - ``names`` - names of ring variables, may be a string or
      list/tuple

    - ``order`` - term order (default: lex)

    EXAMPLES::

        sage: R.<x, y, z> = BooleanPolynomialRing()
        sage: R
        Boolean PolynomialRing in x, y, z

    ::

        sage: p = x*y + x*z + y*z
        sage: x*p
        x*y*z + x*y + x*z

    ::

        sage: R.term_order()
        Lexicographic term order

    ::

        sage: R = BooleanPolynomialRing(5,'x',order='deglex(3),deglex(2)')
        sage: R.term_order()
        Block term order with blocks:
        (Degree lexicographic term order of length 3,
         Degree lexicographic term order of length 2)

    ::

        sage: R = BooleanPolynomialRing(3,'x',order='deglex')
        sage: R.term_order()
        Degree lexicographic term order

    TESTS::

        sage: P.<x0, x1, x2, x3> = BooleanPolynomialRing(4,order='deglex(2),deglex(2)')
        sage: x0 > x1
        True
        sage: x2 > x3
        True
        sage: TestSuite(P).run()

    Boolean polynomial rings are unique parent structures. We
    thus have::

        sage: P.<x,y> = BooleanPolynomialRing(2)
        sage: R.<x,y> = BooleanPolynomialRing(2)
        sage: P is R
        True

    ::

        sage: Q.<x,z> = BooleanPolynomialRing(2)
        sage: P == Q
        False

    ::

        sage: S.<x,y> = BooleanPolynomialRing(2, order='deglex')
        sage: P == S
        False


    """
    def __init__(self, n=None, names=None, order='lex'):
        """
        Create a new boolean polynomial ring.

        EXAMPLES::

            sage: R.<x, y, z> = BooleanPolynomialRing()
            sage: R
            Boolean PolynomialRing in x, y, z

        .. NOTE::

            See class documentation for parameters.
        """
        cdef Py_ssize_t i, j, bstart, bsize

        if names is None:
            raise TypeError("You must specify the names of the variables.")

        if n is None:
            if isinstance(names, (tuple, list)):
                n = len(names)

        try:
            n = int(n)
        except TypeError as msg:
            raise TypeError("Number of variables must be an integer")

        if n < 1:
            raise ValueError("Number of variables must be greater than 1.")

        self.pbind = <Py_ssize_t*>sig_malloc(n*sizeof(Py_ssize_t))

        order = TermOrder(order, n)

        try:
            pb_order_code = order_mapping[order[0].name()]
        except KeyError:
            raise ValueError("Only order keys " +
                             ', '.join(order_mapping.keys()) +
                             " are supported.")

        if order.is_block_order():
            if pb_order_code is pblp:
                raise ValueError("Only deglex and degneglex are supported for block orders.")
            elif pb_order_code is pbdlex:
                pb_order_code = pbblock_dlex
            elif pb_order_code is pbdp_asc:
                pb_order_code = pbblock_dp_asc
            elif pb_order_code is pbdp:
                pb_order_code = pbblock_dp
            for i in range(1, len(order.blocks())):
                if order[0].name() != order[i].name():
                    raise ValueError("Each block must have the same order type "
                                     "(deglex and degneglex) for block orders.")

        if pb_order_code is pbdp:
            for i from 0 <= i < n:
                self.pbind[i] = n - i -1
            pb_order_code = pbdp_asc
        elif pb_order_code is pbblock_dp:
            bstart = 0
            for i from 0 <= i < len(order.blocks()):
                bsize = len(order[i])
                for j from 0 <= j < bsize:
                    self.pbind[bstart + j] = bstart + bsize - j -1
                bstart += bsize
            pb_order_code = pbblock_dp_asc
        else:                           # native PolyBoRi ordering
            for i from 0 <= i < n:
                self.pbind[i] = i

        self._pbring = PBRing(n, pb_order_code)

        if isinstance(names, str):
            pbnames = None
        else:
            pbnames = tuple(names)
            names = [name.replace('(','').replace(')','') for name in pbnames]

        MPolynomialRing_base.__init__(self, GF(2), n, names, order)

        counter = 0
        for i in range(len(order.blocks())-1):
            counter += len(order[i])
            self._pbring.ordering().appendBlock(counter)

        if pbnames is None:
            pbnames = self._names

        for i from 0 <= i < n:
            _n = str_to_bytes(pbnames[self.pbind[i]])
            self._pbring.setVariableName(i, _n)

        self._zero_element = new_BP(self)
        (<BooleanPolynomial>self._zero_element)._pbpoly = \
                                 PBBoolePolynomial(0, self._pbring)
        self._one_element  = new_BP(self)
        (<BooleanPolynomial>self._one_element)._pbpoly = \
                                 PBBoolePolynomial(1, self._pbring)

        self._monom_monoid = BooleanMonomialMonoid(self)

        self.__interface = {}

    def __dealloc__(self):
        sig_free(self.pbind)

    def __reduce__(self):
        """
        EXAMPLES::

            sage: P.<a,b> = BooleanPolynomialRing(2)
            sage: loads(dumps(P)) == P # indirect doctest
            True
        """
        n = self.ngens()
        names = self.variable_names()
        order = self.term_order()
        return unpickle_BooleanPolynomialRing,(n, names, order)

    def ngens(self):
        """
        Return the number of variables in this boolean polynomial ring.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P.ngens()
            2

        ::

            sage: P = BooleanPolynomialRing(1000, 'x')
            sage: P.ngens()
            1000
        """
        return self._pbring.nVariables()

    def gen(self, i=0):
        """
        Return the i-th generator of this boolean polynomial ring.

        INPUT:

        -  ``i`` - an integer or a boolean monomial in one
           variable

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P.gen()
            x
            sage: P.gen(2)
            z
            sage: m = x.monomials()[0]
            sage: P.gen(m)
            x

        TESTS::

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: P.gen(0)
            x
        """
        if isinstance(i, BooleanMonomial):
            if len(i) == 1:
                i = i.index()
            else:
                raise TypeError("Boolean monomials must be in one variable only.")
        cdef idx = int(i)
        if idx < 0 or idx >= self._pbring.nVariables():
            raise ValueError("Generator not defined.")
        return new_BP_from_PBVar(self, self._pbring.variable(self.pbind[idx]))

    def gens(self):
        """
        Return the tuple of variables in this ring.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P.gens()
            (x, y, z)

        ::

            sage: P = BooleanPolynomialRing(10,'x')
            sage: P.gens()
            (x0, x1, x2, x3, x4, x5, x6, x7, x8, x9)

        """
        return tuple(new_BP_from_PBVar(self,
                                       self._pbring.variable(self.pbind[i]))
                     for i in range(self.__ngens))

    def change_ring(self, base_ring=None, names=None, order=None):
        """
        Return a new multivariate polynomial ring with base ring
        ``base_ring``, variable names set to ``names``, and term
        ordering given by ``order``.

        When ``base_ring`` is not specified, this function returns
        a ``BooleanPolynomialRing`` isomorphic to ``self``. Otherwise,
        this returns a ``MPolynomialRing``. Each argument above is
        optional.

        INPUT:

        - ``base_ring`` -- a base ring
        - ``names`` -- variable names
        - ``order`` -- a term order

        EXAMPLES::

            sage: P.<x, y, z> = BooleanPolynomialRing()
            sage: P.term_order()
            Lexicographic term order
            sage: R = P.change_ring(names=('a', 'b', 'c'), order="deglex")
            sage: R
            Boolean PolynomialRing in a, b, c
            sage: R.term_order()
            Degree lexicographic term order
            sage: T = P.change_ring(base_ring=GF(3))
            sage: T
            Multivariate Polynomial Ring in x, y, z over Finite Field of size 3
            sage: T.term_order()
            Lexicographic term order
        """

        if names is None:
            names = self.variable_names()
        if order is None:
            order = self.term_order()

        if base_ring is None:
            from sage.rings.polynomial.polynomial_ring_constructor import BooleanPolynomialRing_constructor
            return BooleanPolynomialRing_constructor(names=names, order=order)
        else:
            return PolynomialRing(base_ring, self.ngens(), names, order=order)

    def _repr_(self):
        """
        EXAMPLES::

            sage: P.<x, y> = BooleanPolynomialRing(2)
            sage: P # indirect doctest
            Boolean PolynomialRing in x, y
        """
        # we use this function when we throw exceptions, thus we want
        # it to be fast.
        if self._repr is None:
            gens = ", ".join(self._names)
            self._repr = "Boolean PolynomialRing in %s" % (gens)
        return self._repr

    # Coercion
    cpdef _coerce_map_from_(self,S):
        """
        There is coercion from the base ring, from any boolean
        polynomial ring with compatible variable names,
        any boolean monomial monoid with compatible variable
        names, and any polynomial ring with compatible variable
        names and base ring.

        Before :trac:`9138`, boolean polynomial rings had
        a custom containment test, but that is not needed now
        since it now uses Sage's new coercion model. So, we
        move the tests from the old ``__contains__`` to here.

        TESTS::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: a in B
            True

        Any boolean monomial is contained in the ring::

            sage: e = B.random_element(); e
            a*b + a*c + a + b*d + 1
            sage: e.lt()
            a*b
            sage: e.lt().parent()
            MonomialMonoid of Boolean PolynomialRing in a, b, c, d
            sage: e.lt() in B   # indirect doctest
            True

        Note that all integers are considered to be in the boolean
        polynomial ring::

            sage: 0 in B
            True
            sage: 1 in B
            True
            sage: 7 in B
            True
            sage: 7 in GF(2)
            True

        We test that :trac:`10173` is fixed::

            sage: R = BooleanPolynomialRing(256,'x')
            sage: S = PolynomialRing(GF(2),256,'y')
            sage: S.gen(8) in R
            False

        Of course, coercion is also responsible for arithmetics
        involving different rings. There is coercion from uni- and
        multivariate polynomial rings whose base rings coerce into
        ``GF(2)``::

            sage: ZZ['a','b'].gen() + c
            a + c
            sage: ZZ['a'].gen() + c
            a + c

        Check that :trac:`13284` is fixed::

            sage: from sage.rings.ideal import Cyclic
            sage: R = BooleanPolynomialRing(10, 'x')
            sage: I = Cyclic(R)
            sage: len(I.groebner_basis())
            10
        """
        if self._base.has_coerce_map_from(S):
            return True
        if isinstance(S, (MPolynomialRing_base, PolynomialRing_general,
                          BooleanMonomialMonoid)):
            try:
                get_var_mapping(self, S)
            except NameError:
                return False
            return self._base.has_coerce_map_from(S.base())

    cdef _convert(self, other):
        r"""
        Canonical conversion of elements from other domains to
        this boolean polynomial ring.

        EXAMPLES:

        Convert elements of ``self``.

        ::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: p = x*y + x
            sage: P(p)
            x*y + x

        Convert from monomials over the same ring.

        ::

            sage: P(p.lm())  # indirect doctest
            x*y

        Convert from a different BooleanPolynomialRing.

        ::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: R = BooleanPolynomialRing(2,'y,x')
            sage: p = R(x+y+x*y+1)
            sage: p.parent()
            Boolean PolynomialRing in y, x
            sage: p
            y*x + y + x + 1

        Convert from polynomials over the integers.

        ::

            sage: P = BooleanPolynomialRing(3,'x,y,z')
            sage: R.<z,x,y> = ZZ['z,x,y']
            sage: t = x^2*z+5*y^3
            sage: p = P(t)
            sage: p.parent()
            Boolean PolynomialRing in x, y, z
            sage: p
            x*z + y

        Convert from integers.

        ::

            sage: P = BooleanPolynomialRing(3,'x,y,z')
            sage: p = P(1)
            sage: p.is_one()
            True
            sage: p = P(6)
            sage: p.is_zero()
            True

        Conversion from GF(2).

        ::

            sage: P = BooleanPolynomialRing(3,'x,y,z')
            sage: F = GF(2)
            sage: p = P(F.zero())
            sage: p.is_zero()
            True
            sage: p = P(F.one())
            sage: p.is_one()
            True

        Conversion from boolean monomials over a different boolean
        polynomial ring.

        ::

            sage: R.<y,x> = BooleanPolynomialRing(2)
            sage: M = R._monom_monoid
            sage: P = BooleanPolynomialRing(3,'x,y,z')
            sage: t = P(M(x*y))
            sage: t
            x*y
            sage: t.parent()
            Boolean PolynomialRing in x, y, z

        TESTS::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: R = BooleanPolynomialRing(1,'y')
            sage: p = R(x+y+x*y+1)
            Traceback (most recent call last):
            ...
            TypeError: cannot convert polynomial x*y + x + y + 1 to Boolean PolynomialRing in y: name x not defined

        ::

            sage: P = BooleanPolynomialRing(2,'x,y')
            sage: R.<z,x,y> = ZZ['z,x,y']
            sage: t = x^2*z+5*y^3
            sage: p = P(t)
            Traceback (most recent call last):
            ...
            TypeError: cannot convert polynomial z*x^2 + 5*y^3 to Boolean PolynomialRing in x, y: name z not defined

        Test conversion from a ring that compares equal.

        ::

            sage: P = BooleanPolynomialRing(2,'x,y')
            sage: R.<x,y> = BooleanPolynomialRing(2)
            sage: P == R
            True
            sage: P(x)
            x

        Test that :trac:`10797` is really fixed::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: I = ideal(a*b + a + b*e + c*e + 1, a + b + c*d + c + 1, a*c + c + d*f + d + 1, a*c + c*f + c + d*f + 1, c*f + c + d + e + 1, a + b*c + b*d + e*f + 1)
            sage: I.groebner_basis()
            [1]
        """
        cdef BooleanPolynomial p
        # we check for other PolyBoRi types first since this conversion
        # is used by the PolyBoRi python code often
        if isinstance(other, BooleSet):
            other = new_BP_from_PBSet(other.ring(), (<BooleSet>other)._pbset)

        if isinstance(other, (int, Integer)):
            if other % 2:
                return self._one_element
            else:
                return self._zero_element
        elif isinstance(other, BooleanMonomial):
            if (<BooleanMonomial>other)._ring is self:
                p = new_BP_from_PBMonom(self, (<BooleanMonomial>other)._pbmonom)
                return p
            elif (<BooleanMonomial>other)._parent.ngens() <= \
                    self._pbring.nVariables():
                try:
                    var_mapping = get_var_mapping(self, other.parent())
                except NameError as msg:
                    raise TypeError("cannot coerce monomial %s to %s: %s" % (other, self, msg))
                p = self._one_element
                for i in other.iterindex():
                    p *= var_mapping[i]
                return p
            else:
                raise TypeError("cannot coerce monomial %s to %s" % (other, self))

        elif isinstance(other, BooleanPolynomial) and \
            ((<BooleanPolynomialRing>(<BooleanPolynomial>other)\
            ._parent)._pbring.nVariables() <= self._pbring.nVariables()):
                    # try PolyBoRi's built-in coercions
                    if self._pbring.hash() == \
                            (<BooleanPolynomialRing>(<BooleanPolynomial>other)._parent)._pbring.hash():
                        _tmp = self._pbring.coerce((<BooleanPolynomial>other)._pbpoly)
                        return new_BP_from_PBPoly(self, _tmp)
                    try:
                        var_mapping = get_var_mapping(self, other.parent())
                    except NameError as msg:
                        raise TypeError("cannot coerce polynomial %s to %s: %s" % (other, self, msg))
                    p = self._zero_element
                    for monom in other:
                        new_monom = self._monom_monoid._one_element
                        for i in monom.iterindex():
                            new_monom *= var_mapping[i]
                        p += new_monom
                    return p
        elif isinstance(other, (MPolynomial, Polynomial)) and \
                self.base_ring().has_coerce_map_from(other.base_ring()) and \
                (other.parent().ngens() <= self._pbring.nVariables()):
                    try:
                        var_mapping = get_var_mapping(self, other.parent())
                    except NameError as msg:
                        raise TypeError("cannot coerce polynomial %s to %s: %s" % (other, self, msg))
                    p = self._zero_element
                    exponents = other.exponents()
                    coefs = other.coefficients()
                    for i in range(len(coefs)):
                        if self._base(coefs[i]).is_one():
                            m = self._monom_monoid._one_element
                            for j in range(len(exponents[i])):
                                if exponents[i][j] > 0:
                                    m *= var_mapping[j]
                            p += m
                    return p

        elif isinstance(other, Element) and \
                self.base_ring().has_coerce_map_from(other.parent()):
                    if self.base_ring()(other).is_zero():
                        return self._zero_element
                    else:
                        return self._one_element
        else:
            raise TypeError("cannot coerce from %s to %s" %
                            (type(other), str(self)))

    def _element_constructor_(self, other):
        """
        Convert ``other`` to this Boolean polynomial ring.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(5)    # indirect doctest
            1

            sage: P(x+y)
            x + y

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: R = BooleanPolynomialRing(1,'y')
            sage: p = R(y); p
            y
            sage: p.parent()
            Boolean PolynomialRing in y

            sage: P = BooleanPolynomialRing(2,'x,y')
            sage: R.<z,x,y> = ZZ['z,x,y']
            sage: t = x^2*y + 5*y^3
            sage: p = P(t); p
            x*y + y
            sage: p.parent()
            Boolean PolynomialRing in x, y

        TESTS::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: R = BooleanPolynomialRing(1,'y')
            sage: p = R(x+y+x*y+1)
            Traceback (most recent call last):
            ...
            TypeError: cannot convert polynomial x*y + x + y + 1 to Boolean PolynomialRing in y: name x not defined

            sage: P = BooleanPolynomialRing(2,'x,y')
            sage: R.<z,x,y> = ZZ[]
            sage: t = x^2*z+5*y^3
            sage: p = P(t)
            Traceback (most recent call last):
            ...
            TypeError: cannot convert polynomial z*x^2 + 5*y^3 to Boolean PolynomialRing in x, y: name z not defined

        We test that univariate polynomials convert into the
        boolean polynomial ring (:trac:`9138`)::

            sage: R.<x> = ZZ[]
            sage: p = x^3+2*x^2+x+1
            sage: P(p)
            x
        """
        cdef int i

        try:
            return self._convert(other)
        except TypeError:
            pass

        if isinstance(other, BooleanMonomial) and (
                (<BooleanMonomial>other)._pbmonom.deg() <=
                 <Py_ssize_t>self._pbring.nVariables()):
            try:
                var_mapping = get_var_mapping(self, other)
            except NameError as msg:
                raise TypeError("cannot convert monomial %s to %s: %s" % (other, self, msg))
            p = self._one_element
            for i in other.iterindex():
                p *= var_mapping[i]
            return p
        elif isinstance(other, BooleanPolynomial) and \
                ((<BooleanPolynomial>other)._pbpoly.nUsedVariables() <=
                 self._pbring.nVariables()):
            try:
                var_mapping = get_var_mapping(self, other)
            except NameError as msg:
                raise TypeError("cannot convert polynomial %s to %s: %s" % (other, self, msg))
            p = self._zero_element
            for monom in other:
                new_monom = self._monom_monoid._one_element
                for i in monom.iterindex():
                    new_monom *= var_mapping[i]
                p += new_monom
            return p
        elif (isinstance(other, (MPolynomial, Polynomial))) and \
                self.base_ring().has_coerce_map_from(other.base_ring()):
            try:
                var_mapping = get_var_mapping(self, other)
            except NameError as msg:
                raise TypeError("cannot convert polynomial %s to %s: %s" % (other, self, msg))
            p = self._zero_element
            exponents = other.exponents()
            coefs = other.coefficients()
            if isinstance(other, Polynomial):
                # we have a univariate polynomial.
                # That case had only been implemented
                # in trac ticket #9138:
                for i in range(len(coefs)):
                    if self._base(coefs[i]).is_one():
                        p += var_mapping[0]
                return p

            for i in range(len(coefs)):
                if self._base(coefs[i]).is_one():
                    m = self._monom_monoid._one_element
                    for j in range(len(exponents[i])):
                        if exponents[i][j] > 0:
                            m *= var_mapping[j]
                    p += m
            return p
        elif isinstance(other, SingularElement):
            other = str(other)

        if isinstance(other, str):
            gd = self.gens_dict()
            if other in gd:
                return gd[other]
            other = other.replace("^","**")
            p = self(eval(other, gd, {}))
            return p

        try:
            i = int(other)
        except Exception:
            try:    # last chance: try Sage's conversions over GF(2), Trac #13284
                return self._convert(self.cover_ring()(other))
            except Exception:
                raise TypeError("cannot convert %s to BooleanPolynomial" % (type(other)))

        if i % 2:
            return self._one_element
        else:
            return self._zero_element

    def __hash__(self):
        """
        Return a hash of this boolean polynomial ring.

        EXAMPLES::

            sage: P.<a,b,c,d> = BooleanPolynomialRing(4, order='lex')
            sage: P
            Boolean PolynomialRing in a, b, c, d
            sage: {P:1} # indirect doctest
            {Boolean PolynomialRing in a, b, c, d: 1}
        """
        cdef long _hash = hash(self.variable_names()) ^ 42
        _hash ^= hash(self.term_order())
        return _hash

    def remove_var(self, *var, order=None):
        """
        Remove a variable or sequence of variables from this ring.

        If ``order`` is not specified, then the subring inherits the
        term order of the original ring, if possible.

        EXAMPLES::

            sage: R.<x,y,z,w> = BooleanPolynomialRing()
            sage: R.remove_var(z)
            Boolean PolynomialRing in x, y, w
            sage: R.remove_var(z,x)
            Boolean PolynomialRing in y, w
            sage: R.remove_var(y,z,x)
            Boolean PolynomialRing in w

        Removing all variables results in the base ring::

            sage: R.remove_var(y,z,x,w)
            Finite Field of size 2

        If possible, the term order is kept:

             sage: R.<x,y,z,w> = BooleanPolynomialRing(order='deglex')
             sage: R.remove_var(y).term_order()
             Degree lexicographic term order

             sage: R.<x,y,z,w> = BooleanPolynomialRing(order='lex')
             sage: R.remove_var(y).term_order()
             Lexicographic term order

        Be careful with block orders when removing variables::

            sage: R.<x,y,z,u,v> = BooleanPolynomialRing(order='deglex(2),deglex(3)')
            sage: R.remove_var(x,y,z)
            Traceback (most recent call last):
            ...
            ValueError: impossible to use the original term order (most likely because it was a block order). Please specify the term order for the subring
            sage: R.remove_var(x,y,z, order='deglex')
            Boolean PolynomialRing in u, v

        """
        vars = list(self.variable_names())
        for v in var:
            vars.remove(str(v))
        if len(vars) == 0:
            return self.base_ring()
        if order is None:
            try:
                return BooleanPolynomialRing(names=vars, order=self.term_order())
            except ValueError:
                raise ValueError("impossible to use the original term order (most likely because it was a block order). Please specify the term order for the subring")
        else:
            return BooleanPolynomialRing(names=vars, order=order)

    def ideal(self, *gens, **kwds):
        """
        Create an ideal in this ring.

        INPUT:


        -  ``gens`` - list or tuple of generators

        -  ``coerce`` - bool (default: True) automatically
           coerce the given polynomials to this ring to form the ideal


        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P.ideal(x+y)
            Ideal (x + y) of Boolean PolynomialRing in x, y, z

        ::

            sage: P.ideal(x*y, y*z)
            Ideal (x*y, y*z) of Boolean PolynomialRing in x, y, z

        ::

            sage: P.ideal([x+y, z])
            Ideal (x + y, z) of Boolean PolynomialRing in x, y, z
        """
        from sage.misc.flatten import flatten
        coerce = kwds.get('coerce', True)
        gens = flatten(gens)
        return BooleanPolynomialIdeal(self, gens, coerce)

    def random_element(self, degree=None, terms=None, choose_degree=False, vars_set=None):
        """
        Return a random boolean polynomial. Generated polynomial has the
        given number of terms, and at most given degree.

        INPUT:

        -  ``degree`` - maximum degree (default: 2 for len(var_set) > 1, 1 otherwise)

        -  ``terms`` -- number of terms requested (default: 5). If more
           terms are requested than exist, then this parameter is
           silently reduced to the maximum number of available terms.

        -  ``choose_degree`` - choose degree of monomials
           randomly first, rather than monomials uniformly random

        -  ``vars_set`` - list of integer indices of
           generators of self to use in the generated polynomial


        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P.random_element(degree=3, terms=4)
            x*y*z + x*z + x + y*z

        ::

            sage: P.random_element(degree=1, terms=2)
            z + 1

        In corner cases this function will return fewer terms by default::

            sage: P = BooleanPolynomialRing(2,'y')
            sage: P.random_element()
            y0*y1 + y0

            sage: P = BooleanPolynomialRing(1,'y')
            sage: P.random_element()
            y

        We return uniformly random polynomials up to degree 2::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: B.random_element(terms=Infinity)
            a*b + a*c + a*d + b*c + b*d + d

        TESTS::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P.random_element(degree=4)
            Traceback (most recent call last):
            ...
            ValueError: Given degree should be less than or equal to number of variables (3)

            sage: P.random_element(degree=1, terms=5)
            y + 1

            sage: P.random_element(degree=2, terms=5, vars_set=(0,1))
            x*y + y

        We test that :trac:`13845` is fixed::

            sage: n = 10
            sage: B = BooleanPolynomialRing(n, 'x')
            sage: r = B.random_element(terms=(n/2)**2)
        """
        from sage.rings.integer import Integer
        from sage.arith.all import binomial

        if not vars_set:
            vars_set=range(self.ngens())
        nvars = len(vars_set)

        if terms is None:
            if nvars > 2:
                terms = 5
            elif nvars == 2:
                terms = 2
            elif nvars == 1:
                terms = 1

        if degree is None:
            if nvars > 1:
                degree = 2
            else:
                degree = 1
        else:
            degree = Integer(degree)

        if degree > nvars:
            raise ValueError("Given degree should be less than or equal to number of variables (%s)" % nvars)

        tot_terms=0
        monom_counts = []
        for i from 0 <= i <= degree:
            tot_terms += binomial(nvars,i)
            monom_counts.append(tot_terms)

        if terms > tot_terms:
            terms = tot_terms//2 + (tot_terms%2)
        else:
            terms = Integer(terms)

        p = self._zero_element
        while len(p) < terms:
            p=self(p.set().union(\
                self._random_uniform_rec(degree, monom_counts, vars_set, choose_degree, terms-len(p))\
                .set()))
        return p

    def _random_uniform_rec(self, degree, monom_counts, vars_set, dfirst, l):
        r"""
        Recursively generate a random polynomial in this ring, using the
        variables from ``vars_set``.

        INPUT:


        -  ``degree`` - maximum degree

        -  ``monom_counts`` - a list containing total number
           of monomials up to given degree

        -  ``vars_set`` - list of variable indices to use in
           the generated polynomial

        -  ``dfirst`` - if ``True`` choose degree
           first, otherwise choose the monomial uniformly

        -  ``l`` - number of monomials to generate


        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P._random_uniform_rec(2, [1, 3, 4], (0,1), True, 2)
            x + y
            sage: P._random_uniform_rec(2, [1, 3, 4], (0,1), True, 2)
            0
        """
        from sage.rings.integer import Integer
        from sage.rings.integer_ring import ZZ
        if l == 0:
            return self._zero_element
        if l == 1:
            if dfirst:
                return self._random_monomial_dfirst(degree, vars_set)
            else:
                return self._random_monomial_uniform(monom_counts, vars_set)

        return self._random_uniform_rec(degree, monom_counts,
                    vars_set, dfirst, l//2) + \
               self._random_uniform_rec(degree, monom_counts,
                    vars_set, dfirst, l - l//2)

    def _random_monomial_uniform(self, monom_counts, vars_set):
        r"""
        Choose a random monomial uniformly from set of monomials in the
        variables indexed by ``vars_set`` in self.

        INPUT:


        -  ``monom_counts`` - list of number of monomials up
           to given degree

        -  ``vars_set`` - list of variable indices to use in
           the generated monomial


        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: [P._random_monomial_uniform([1, 3, 4], (0,1)) for _ in range(10)]
            [x*y, x*y, x, x, x, x*y, x, y, x*y, 1]
        """
        from sage.rings.integer_ring import ZZ
        from sage.combinat.combination import from_rank

        t = ZZ.random_element(0,monom_counts[-1])
        if t == 0:
            return self._one_element
        i = 1
        while t >= monom_counts[i]:
            i+=1
        mind = t-monom_counts[i-1]
        var_inds = from_rank(mind,len(vars_set),i)
        M = self._monom_monoid
        m = M._one_element
        for j in var_inds:
            m*=M.gen(vars_set[j])
        return self(m)

    def _random_monomial_dfirst(self, degree, vars_set):
        r"""
        Choose a random monomial using variables indexed in
        ``vars_set`` up to given ``degree``. The
        degree of the monomial, `d`, is chosen uniformly in the
        interval [0,degree] first, then the monomial is generated by
        selecting a random sample of size `d` from
        ``vars_set``.

        INPUT:


        -  ``degree`` - maximum degree

        -  ``vars_set`` - list of variable indices of self


        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: [P._random_monomial_dfirst(3, (0,1,2)) for _ in range(10)]  # py2
            [x*y*z, x*y*z, x*y*z, y*z, x*z, z, z, y*z, x*y*z, 1]
            sage: [P._random_monomial_dfirst(3, (0,1,2)) for _ in range(10)]  # py3 random
            [x*y*z, x*y*z, x*y*z, x*y, x*z, x, x, y*z, x*y*z, 1]
        """
        from sage.rings.integer_ring import ZZ
        sample = current_randstate().python_random().sample
        d = ZZ.random_element(0, degree + 1)
        vars = sample(vars_set, d)
        M = self._monom_monoid
        m = M._one_element
        for j in vars:
            m *= M.gen(j)
        return self(m)

    def cover_ring(self):
        r"""
        Return `R = \GF{2}[x_1,x_2,...,x_n]` if ``x_1,x_2,...,x_n`` is
        the ordered list of variable names of this ring. ``R`` also
        has the same term ordering as this ring.

        EXAMPLES::

            sage: B.<x,y> = BooleanPolynomialRing(2)
            sage: R = B.cover_ring(); R
            Multivariate Polynomial Ring in x, y over Finite Field of size 2

        ::

            sage: B.term_order() == R.term_order()
            True

        The cover ring is cached::

            sage: B.cover_ring() is B.cover_ring()
            True
        """
        if self.__cover_ring is not None:
            return self.__cover_ring
        R = PolynomialRing(GF(2), self.ngens(),
                           self.variable_names(), order=self.term_order())
        self.__cover_ring = R
        return R

    def defining_ideal(self):
        """
        Return `I = <x_i^2 + x_i> \subset R` where ``R =
        self.cover_ring()``, and `x_i` any element in the set of
        variables of this ring.

        EXAMPLES::

            sage: B.<x,y> = BooleanPolynomialRing(2)
            sage: I = B.defining_ideal(); I
            Ideal (x^2 + x, y^2 + y) of Multivariate Polynomial Ring
            in x, y over Finite Field of size 2
        """
        R = self.cover_ring()
        G = R.gens()
        return R.ideal([x**2 + x for x in G])

    def _singular_init_(self, singular=singular_default):
        r"""
        Return a newly created Singular quotient ring matching this boolean
        polynomial ring.

        .. NOTE::

           TODO: This method does not only return a string but actually
           calls Singular.

        EXAMPLES::

            sage: B.<x,y> = BooleanPolynomialRing(2)
            sage: B._singular_() # indirect doctest
            polynomial ring, over a field, global ordering
            //   coefficients: ZZ/2
            //   number of vars : 2
            //        block   1 : ordering lp
            //                  : names    x y
            //        block   2 : ordering C
            // quotient ring from ideal
            _[1]=x2+x
            _[2]=y2+y
        """
        return self.cover_ring().quo(self.defining_ideal())._singular_init_()

    def _magma_init_(self, magma):
        """
        Return a string which when evaluated with Magma returns a
        Magma representation of this boolean polynomial ring.

        INPUT:

        -  ``magma`` - a magma instance

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: magma(B)                               # indirect doctest; optional - magma
            Boolean polynomial ring of rank 3 over GF(2)
            Order: Lexicographical (bit vector word)
            Variables: x, y, z
        """
        #R = magma(self.cover_ring())
        #v = [z.name() for z in R.gens()]  # important to use this because it caches the generators
        #w = [f._repr_with_changed_varnames(v) for f in self.defining_ideal().gens()]
        #return "quo<%s | %s>" % (R.name(), ",".join(w))
        s = 'BooleanPolynomialRing(%s,%s)' % (self.ngens(), self.term_order().magma_str())
        return magma._with_names(s, self.variable_names())

    def interpolation_polynomial(self, zeros, ones):
        r"""
        Return the lexicographically minimal boolean polynomial for the
        given sets of points.

        Given two sets of points ``zeros`` - evaluating to zero
        - and ``ones`` - evaluating to one -, compute the
        lexicographically minimal boolean polynomial satisfying these
        points.

        INPUT:


        -  ``zeros`` - the set of interpolation points mapped
           to zero

        -  ``ones`` - the set of interpolation points mapped to
           one


        EXAMPLES:

        First we create a random-ish boolean polynomial.

        ::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing(6)
            sage: f = a*b*c*e + a*d*e + a*f + b + c + e + f + 1

        Now we find interpolation points mapping to zero and to one.

        ::

            sage: zeros = set([(1, 0, 1, 0, 0, 0), (1, 0, 0, 0, 1, 0),
            ....:              (0, 0, 1, 1, 1, 1), (1, 0, 1, 1, 1, 1),
            ....:              (0, 0, 0, 0, 1, 0), (0, 1, 1, 1, 1, 0),
            ....:              (1, 1, 0, 0, 0, 1), (1, 1, 0, 1, 0, 1)])
            sage: ones = set([(0, 0, 0, 0, 0, 0), (1, 0, 1, 0, 1, 0),
            ....:             (0, 0, 0, 1, 1, 1), (1, 0, 0, 1, 0, 1),
            ....:             (0, 0, 0, 0, 1, 1), (0, 1, 1, 0, 1, 1),
            ....:             (0, 1, 1, 1, 1, 1), (1, 1, 1, 0, 1, 0)])
            sage: [f(*p) for p in zeros]
            [0, 0, 0, 0, 0, 0, 0, 0]
            sage: [f(*p) for p in ones]
            [1, 1, 1, 1, 1, 1, 1, 1]

        Finally, we find the lexicographically smallest interpolation
        polynomial using PolyBoRi .

        ::

            sage: g = B.interpolation_polynomial(zeros, ones); g
            b*f + c + d*f + d + e*f + e + 1

        ::

            sage: [g(*p) for p in zeros]
            [0, 0, 0, 0, 0, 0, 0, 0]
            sage: [g(*p) for p in ones]
            [1, 1, 1, 1, 1, 1, 1, 1]

        Alternatively, we can work with PolyBoRi's native
        ``BooleSet``'s. This example is from the PolyBoRi tutorial::

            sage: B = BooleanPolynomialRing(4,"x0,x1,x2,x3")
            sage: x = B.gen
            sage: V=(x(0)+x(1)+x(2)+x(3)+1).set(); V
            {{x0}, {x1}, {x2}, {x3}, {}}
            sage: f=x(0)*x(1)+x(1)+x(2)+1
            sage: z = f.zeros_in(V); z
            {{x1}, {x2}}
            sage: o = V.diff(z); o
            {{x0}, {x3}, {}}
            sage: B.interpolation_polynomial(z,o)
            x1 + x2 + 1

        ALGORITHM: Calls ``interpolate_smallest_lex`` as described in
        the PolyBoRi tutorial.
        """
        #from brial.interpolate import interpolate_smallest_lex
        from sage.misc.misc_c import prod
        n = self.ngens()
        x = self.gens()
        if isinstance(zeros, BooleSet):
            z = zeros
        else:
            z = sum([prod([x[i] for i in xrange(n) if v[i]],
                          self.one()) for v in zeros],
                    self.zero())
            z = z.set()
        if isinstance(ones, BooleSet):
            o = ones
        else:
            o = sum([prod([x[i] for i in xrange(n) if v[i]],
                          self.one()) for v in ones],
                    self.zero())
            o = o.set()
        return interpolate_smallest_lex(z, o)

###
#
# Methods for compatibility with PolyBoRi
#
###

    def id(self):
        """
        Return a unique identifier for this boolean polynomial ring.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: print("id: {}".format(P.id()))
            id: ...

        ::

            sage: P = BooleanPolynomialRing(10, 'x')
            sage: Q = BooleanPolynomialRing(20, 'x')

            sage: P.id() != Q.id()
            True
        """
        return self._pbring.id()

    def variable(self, i=0):
        """
        Return the i-th generator of this boolean polynomial ring.

        INPUT:

        - ``i`` - an integer or a boolean monomial in one variable

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: P.variable()
            x
            sage: P.variable(2)
            z
            sage: m = x.monomials()[0]
            sage: P.variable(m)
            x

        TESTS::

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: P.variable(0)
            x
        """
        if isinstance(i, BooleanMonomial):
            if len(i) == 1:
                i = i.index()
            else:
                raise TypeError("Boolean monomials must be in one variable only.")
        i = int(i)
        if i < 0 or i >= self._pbring.nVariables():
            raise ValueError("Generator not defined.")

        return new_BM_from_PBVar(self._monom_monoid, self, self._pbring.variable(self.pbind[i]))

    def get_order_code(self):
        """

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: B.get_order_code()
            0

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing(order='deglex')
            sage: B.get_order_code()
            1

        .. NOTE::


          This function which is part of the PolyBoRi upstream API works
          with a current global ring. This notion is avoided in Sage.
        """
        return self._pbring.ordering().getOrderCode()

    def get_base_order_code(self):
        """

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: B.get_base_order_code()
            0

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing(order='deglex')
            sage: B.get_base_order_code()
            1
            sage: T = TermOrder('deglex',2) + TermOrder('deglex',2)
            sage: B.<a,b,c,d> = BooleanPolynomialRing(4, order=T)
            sage: B.get_base_order_code()
            1

        .. NOTE::

          This function which is part of the PolyBoRi upstream API works
          with a current global ring. This notion is avoided in Sage.
        """
        return self._pbring.ordering().getBaseOrderCode()

    def has_degree_order(self):
        """
        Return checks whether the order code corresponds to a degree ordering.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P.has_degree_order()
            False
        """
        return self._pbring.ordering().isDegreeOrder()

    def _settings(self, names, blocks):
        for (idx, elt) in enumerate(names):
            self._pbring.setVariableName(self.pbind[idx],
                    str_to_bytes(elt))

        for elt in blocks:
            self._pbring.ordering().appendBlock(elt)

    def one(self):
        """
        EXAMPLES::

            sage: P.<x0,x1> = BooleanPolynomialRing(2)
            sage: P.one()
            1
        """
        return self._one_element

    def zero(self):
        """
        EXAMPLES::

            sage: P.<x0,x1> = BooleanPolynomialRing(2)
            sage: P.zero()
            0
        """
        return self._zero_element

    def clone(self, ordering=None, names=[], blocks=[]):
        """
        Shallow copy this boolean polynomial ring, but with different
        ordering, names or blocks if given.

        ring.clone(ordering=..., names=..., block=...) generates a shallow copy
        of ring, but with different ordering, names or blocks if given.

        EXAMPLES::

            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: B.clone()
            Boolean PolynomialRing in a, b, c

        ::

            sage: B.<x,y,z> = BooleanPolynomialRing(3,order='deglex')
            sage: y*z > x
            True

        Now we call the clone method and generate a compatible, but 'lex' ordered, ring::

            sage: C = B.clone(ordering=0)
            sage: C(y*z) > C(x)
            False

        Now we change variable names::

            sage: P.<x0,x1> = BooleanPolynomialRing(2)
            sage: P
            Boolean PolynomialRing in x0, x1

        ::

            sage: Q = P.clone(names=['t'])
            sage: Q
            Boolean PolynomialRing in t, x1

        We can also append blocks to block orderings this way::

            sage: R.<x1,x2,x3,x4> = BooleanPolynomialRing(order='deglex(1),deglex(3)')
            sage: x2 > x3*x4
            False

        Now we call the internal method and change the blocks::

            sage: S = R.clone(blocks=[3])
            sage: S(x2) > S(x3*x4)
            True


        .. NOTE::

            This is part of PolyBoRi's native interface.
        """

        cdef PBRing ring = self._pbring.clone()
        if ordering is not None:
            ring.changeOrdering(ordering)
        for (idx, elt) in enumerate(names):
            ring.setVariableName(self.pbind[idx], str_to_bytes(elt))

        for elt in blocks:
            ring.ordering().appendBlock(elt)
        cdef BooleanPolynomialRing R = BooleanPolynomialRing_from_PBRing(ring)

        return R

    def n_variables(self):
        """
        Return the number of variables in this boolean polynomial ring.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P.n_variables()
            2

        ::

            sage: P = BooleanPolynomialRing(1000, 'x')
            sage: P.n_variables()
            1000

        .. NOTE::

            This is part of PolyBoRi's native interface.
        """
        return self._pbring.nVariables()


def get_var_mapping(ring, other):
    r"""
    Return a variable mapping between variables of
    ``other`` and ``ring``. When other is a
    parent object, the mapping defines images for all variables of
    other. If it is an element, only variables occurring in other are
    mapped.

    Raises ``NameError`` if no such mapping is possible.

    EXAMPLES::

        sage: P.<x,y,z> = BooleanPolynomialRing(3)
        sage: R.<z,y> = QQ[]
        sage: sage.rings.polynomial.pbori.get_var_mapping(P,R)
        [z, y]
        sage: sage.rings.polynomial.pbori.get_var_mapping(P, z^2)
        [z, None]

    ::

        sage: R.<z,x> = BooleanPolynomialRing(2)
        sage: sage.rings.polynomial.pbori.get_var_mapping(P,R)
        [z, x]
        sage: sage.rings.polynomial.pbori.get_var_mapping(P, x^2)
        [None, x]
    """
    my_names = list(ring._names)  # we need .index(.)
    if isinstance(other, (Parent, BooleanMonomialMonoid)):
        indices = list(xrange(other.ngens()))
        ovar_names = other._names
    else:
        ovar_names = other.parent().variable_names()
        if isinstance(other, BooleanPolynomial):
            indices = other.vars_as_monomial().iterindex()
        elif isinstance(other, BooleanMonomial):
            indices = other.iterindex()
        else:
            t = other.variables()
            ovar_names = list(ovar_names)
            indices = [ovar_names.index(str(var)) for var in t]

    var_mapping = [None] * len(ovar_names)
    for idx in indices:
        try:
            ind = int(my_names.index(ovar_names[idx]))
        except ValueError:
            # variable name not found in list of our variables
            # raise an exception and bail out
            raise NameError("name %s not defined" % ovar_names[idx])
        var_mapping[idx] = ring.gen(ind)
    return var_mapping


class BooleanMonomialMonoid(UniqueRepresentation, Monoid_class):
    """
    Construct a boolean monomial monoid given a boolean polynomial
    ring.

    This object provides a parent for boolean monomials.

    INPUT:

    - ``polring`` - the polynomial ring our monomials lie in


    EXAMPLES::

        sage: from brial import BooleanMonomialMonoid
        sage: P.<x,y> = BooleanPolynomialRing(2)
        sage: M = BooleanMonomialMonoid(P)
        sage: M
        MonomialMonoid of Boolean PolynomialRing in x, y

        sage: M.gens()
        (x, y)
        sage: type(M.gen(0))
        <type 'sage.rings.polynomial.pbori.BooleanMonomial'>

    Since :trac:`9138`, boolean monomial monoids are
    unique parents and are fit into the category framework::

        sage: loads(dumps(M)) is M
        True
        sage: TestSuite(M).run()

    """
    def __init__(self, BooleanPolynomialRing polring):
        """
        Create a new boolean polynomial ring.

        TESTS::

            sage: from brial import BooleanMonomialMonoid
            sage: B.<a,b,c> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(B)
            sage: M
            MonomialMonoid of Boolean PolynomialRing in a, b, c


        .. NOTE::

            See class documentation for parameters.
        """
        cdef BooleanMonomial m
        self._ring = polring
        from sage.categories.monoids import Monoids
        Parent.__init__(self, GF(2), names=polring._names, category=Monoids().Commutative())

        m = new_BM(self, polring)
        m._pbmonom = PBMonom(polring._pbring)
        self._one_element = m

    def _repr_(self):
        """
        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: M = BooleanMonomialMonoid(P)
            sage: M # indirect doctest
            MonomialMonoid of Boolean PolynomialRing in x, y
        """
        return "MonomialMonoid of %s" % (str(self._ring))

    def __hash__(self):
        """
        Return a hash for this monoid.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: M = BooleanMonomialMonoid(P)
            sage: {M:1} # indirect doctest
            {MonomialMonoid of Boolean PolynomialRing in x, y: 1}
        """
        return hash(str(self))

    def ngens(self):
        """
        Return the number of variables in this monoid.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P = BooleanPolynomialRing(100, 'x')
            sage: M = BooleanMonomialMonoid(P)
            sage: M.ngens()
            100
        """
        return self._ring.ngens()

    def gen(self, Py_ssize_t i=0):
        """
        Return the i-th generator of ``self``.

        INPUT:

        -  ``i`` - an integer

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M.gen(0)
            x
            sage: M.gen(2)
            z

            sage: P = BooleanPolynomialRing(1000, 'x')
            sage: M = BooleanMonomialMonoid(P)
            sage: M.gen(50)
            x50
        """
        if i < 0 or i >= self.ngens():
            raise ValueError("Generator not defined.")

        cdef PBVar newvar
        newvar = PBBooleVariable(i, (<BooleanPolynomialRing>self._ring)._pbring)

        return new_BM_from_PBVar(self, (<BooleanPolynomialRing>self._ring), newvar)

    def gens(self):
        """
        Return the tuple of generators of this monoid.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M.gens()
            (x, y, z)
        """
        return tuple(self.gen(i) for i in xrange(self.ngens()))

    def _get_action_(self, S, op, bint self_on_left):
        """
        Monomials support multiplication by 0 and 1 in GF(2).

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M.get_action(ZZ) # indirect doctest
            Right action by Integer Ring on MonomialMonoid of Boolean PolynomialRing in x, y, z
            sage: M.get_action(GF(2))
            Right action by Finite Field of size 2 on MonomialMonoid of Boolean PolynomialRing in x, y, z
            sage: M.get_action(QQ) is None
            True
        """
        if GF(2).has_coerce_map_from(S) and op is operator.mul:
            return BooleanMulAction(S, self, not self_on_left, op=op)

    def _coerce_impl(self, other):
        """
        Canonical conversion of elements from other objects to this
        monoid.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: x_monom = M(x); x_monom
            x
            sage: M(x_monom) # indirect doctest
            x

        Convert elements from :class:`BooleanMonomialMonoid` where the
        generators of self include the generators of the other monoid::

            sage: from brial import BooleanMonomialMonoid
            sage: R.<z,y> = BooleanPolynomialRing(2)
            sage: N = BooleanMonomialMonoid(R)
            sage: m = M(N(y*z)); m
            y*z
            sage: m.parent() is M
            True

        TESTS::

            sage: from brial import BooleanMonomialMonoid
            sage: R.<t,y> = BooleanPolynomialRing(2)
            sage: N = BooleanMonomialMonoid(R)
            sage: M(N(y))
            y
            sage: M(N(t))
            Traceback (most recent call last):
            ...
            ValueError: cannot convert monomial t to MonomialMonoid of Boolean PolynomialRing in x, y, z: name t not defined

            sage: from brial import BooleanMonomialMonoid
            sage: R.<t,x,y,z> = BooleanPolynomialRing(4)
            sage: N = BooleanMonomialMonoid(R)
            sage: M(N(x*y*z))
            x*y*z
            sage: M(N(x*y*t))
            Traceback (most recent call last):
            ...
            ValueError: cannot convert monomial t*x*y to MonomialMonoid of Boolean PolynomialRing in x, y, z: name t not defined
        """
        if isinstance(other, BooleanMonomial) and \
            ((<BooleanMonomial>other)._parent.ngens() <= \
            (<BooleanPolynomialRing>self._ring)._pbring.nVariables()):
                try:
                    var_mapping = get_var_mapping(self, other.parent())
                except NameError as msg:
                    raise ValueError("cannot coerce monomial %s to %s: %s" % (other, self, msg))
                m = self._one_element
                for i in other.iterindex():
                    m *= var_mapping[i]
                return m
        raise TypeError("coercion from %s to %s not implemented" %
                        (type(other), str(self)))

    def _element_constructor_(self, other=None):
        """
        Convert elements of other objects to elements of this monoid.

        INPUT:

        - ``other`` - element to convert, if ``None`` a
           :class:`BooleanMonomial` representing 1 is returned only
          :class:`BooleanPolynomial`s with the same parent ring as ``self``
          which have a single monomial is converted

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: x_monom = M(x); x_monom
            x

            sage: M(x*y)
            x*y

            sage: M(x+y)
            Traceback (most recent call last):
            ...
            TypeError: cannot convert to BooleanMonomialMonoid

        Convert elements of self::

            sage: M(x_monom)
            x

        Convert from other :class:`BooleanPolynomialRing`s::

            sage: R.<z,x> = BooleanPolynomialRing(2)
            sage: t = M(z); t
            z
            sage: t.parent() is M
            True

        Convert :class:`BooleanMonomial`s over other
        :class:`BooleanPolynomialRing`s::

            sage: N = BooleanMonomialMonoid(R)
            sage: t = M(N(x*z)); t
            x*z
            sage: t.parent() is M
            True

        Convert :class:`BooleSet`s::

            sage: t = M.an_element(); t
            x
            sage: M(t.set()) == t
            True

        Convert a tuple of integers::

            sage: M((0,2,0))
            x*z

        """
        cdef BooleanMonomial m
        cdef PBMonom t

        # this is needed for the PolyBoRi python code
        if other is None:
            return self._one_element

        #  We must not call this explicitly in an element constructor.
        #  It used to be ok, when there was a custom __call__
        #        try:
        #            return self._coerce_(other)
        #        except ValueError:
        #            pass
        #        except TypeError:
        #            pass

        try:
            return self._coerce_impl(other)
        except (ValueError, TypeError):
            pass

        if isinstance(other, BooleanPolynomial) and \
            (<BooleanPolynomial>other)._pbpoly.isSingleton():
                if (<BooleanPolynomial>other)._parent is self._ring:
                    return new_BM_from_PBMonom(self,
                            (<BooleanPolynomialRing>self._ring),
                            (<BooleanPolynomial>other)._pbpoly.lead())
                elif ((<BooleanPolynomial>other)._pbpoly.nUsedVariables() <= \
                    (<BooleanPolynomialRing>self._ring)._pbring.nVariables()):
                        try:
                            var_mapping = get_var_mapping(self, other)
                        except NameError as msg:
                            raise ValueError("cannot convert polynomial %s to %s: %s" % (other, self, msg))
                        t = (<BooleanPolynomial>other)._pbpoly.lead()

                        m = self._one_element
                        for i in new_BMI_from_BooleanMonomial(other.lm()):
                            m*= var_mapping[i]
                        return m
                else:
                    raise ValueError("cannot convert polynomial %s to %s" % (other, self))

        elif isinstance(other, BooleanMonomial) and \
            ((<BooleanMonomial>other)._pbmonom.deg() <=
             <Py_ssize_t>(<BooleanPolynomialRing>self._ring)._pbring.nVariables()):
                try:
                    var_mapping = get_var_mapping(self, other)
                except NameError as msg:
                    raise ValueError("cannot convert monomial %s to %s: %s" % (other, self, msg))
                m = self._one_element
                for i in other.iterindex():
                    m *= var_mapping[i]
                return m
        elif isinstance(other, BooleSet):
            return self(self._ring(other))
        elif isinstance(other, Element) and \
                self.base_ring().has_coerce_map_from(other.parent()) and \
                        self.base_ring()(other).is_one():
                            return self._one_element
        elif isinstance(other, (int, long)) and other % 2:
            return self._one_element

        elif isinstance(other, (list, set)):
            result = self._one_element
            for elt in other:
                result = result * elt
            return result
        elif isinstance(other, tuple):
            # S.K.: Tuples of integers have not been converted
            # into monomials before. I think that would be very
            # natural (namely the integers providing the index
            # of generators). It is also useful for pickling.
            result = self._one_element
            gens = self.gens()
            for ind in other:
                result *= gens[ind]
            return result

        raise TypeError("cannot convert to BooleanMonomialMonoid")

cdef class BooleanMonomial(MonoidElement):
    """
    Construct a boolean monomial.

    INPUT:

    - ``parent`` - parent monoid this element lives in

    EXAMPLES::

        sage: from brial import BooleanMonomialMonoid, BooleanMonomial
        sage: P.<x,y,z> = BooleanPolynomialRing(3)
        sage: M = BooleanMonomialMonoid(P)
        sage: BooleanMonomial(M)
        1

    .. NOTE::

       Use the :meth:`BooleanMonomialMonoid__call__` method and not
       this constructor to construct these objects.
    """
    def __init__(self, parent):
        """
        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid, BooleanMonomial
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: BooleanMonomial(M)
            1


        .. NOTE::

          See class documentation for parameters.
        """
        self._ring = parent._ring
        self._pbmonom = PBMonom((<BooleanPolynomialRing>self._ring)._pbring)

    def __reduce__(self):
        """
        Pickling

        TESTS::

            sage: from brial import BooleanMonomialMonoid
            sage: R.<z,x> = BooleanPolynomialRing(2)
            sage: M = BooleanMonomialMonoid(R)
            sage: t = M.0*M.1
            sage: loads(dumps(t)) == t   # indirect doctest
            True
        """
        gens = self._parent.gens()
        return self._parent, (tuple(gens.index(x) for x in self.variables()),)

    cpdef int _cmp_(left, right) except -2:
        """
        Compare BooleanMonomial objects.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M(x) < M(y)
            False

            sage: M(x) > M(y)
            True

            sage: M(x) == M(x)
            True

            sage: M(x) <= M(x)
            True

            sage: M(x) >= M(x)
            True
        """
        cdef int res
        res = left._pbmonom.compare((<BooleanMonomial>right)._pbmonom)
        return res

    def _repr_(self):
        """
        Return a string representing this boolean monomial.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: M = sage.rings.polynomial.pbori.BooleanMonomialMonoid(P)
            sage: M(x*y) # indirect doctest
            x*y

            sage: R.<t,u> = BooleanPolynomialRing(2)
            sage: M(x*y)
            x*y
        """
        return ccrepr(self._pbmonom)

    def _eval(self, d):
        """
        Evaluate this monomial.

        INPUT:

        - ``d`` -- dictionary with integer indices

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: m = P._monom_monoid(x*y)
            sage: m._eval({0:y,1:z})
            y*z
        """
        res = 1
        for i in self.iterindex():
            if i in d:
                res *= d[i]
            else:
                res *= self._parent.gen(i)
        return res

    def __call__(self, *args, **kwds):
        """
        Evaluate this monomial.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y
            sage: m = f.lm()
            sage: m(B(0),B(1))
            0
            sage: m(x=B(1))
            y
        """
        P = self.parent()
        if args and kwds:
            raise ValueError("Using keywords and regular arguments not supported.")
        if args:
            d = {}
            if len(args) > self._parent.ngens():
                raise ValueError("Number of arguments is greater than the number of variables of parent ring.")
            for i in range(len(args)):
                d[i] = args[i]
        elif kwds:
            d = list(self._parent.gens())
            gd = dict(zip(self._parent.variable_names(),range(len(d))))
            for var, val in kwds.iteritems():
                d[gd[var]] = val
        res = self._parent._one_element
        for var in self.iterindex():
            res *= d[var]
        return res

    def __hash__(self):
        """
        Return a hash of this monomial.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y
            sage: m = f.lm()
            sage: {m:1} #indirect doctest
            {x*y: 1}
        """
        return <Py_ssize_t>(self._pbmonom.stableHash())

    def stable_hash(self):
        """
        A hash value which is stable across processes.

        EXAMPLES::

            sage: B.<x,y> = BooleanPolynomialRing()
            sage: x.lm() is x.lm()
            False
            sage: x.lm().stable_hash() == x.lm().stable_hash()
            True

        .. NOTE::

           This function is part of the upstream PolyBoRi
           interface. In Sage all hashes are stable.
        """
        return <Py_ssize_t>(self._pbmonom.stableHash())

    def ring(self):
        """
        Return the corresponding boolean ring.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: a.lm().ring() is B
            True
        """
        return self._ring

    def index(self):
        """
        Return the variable index of the first variable in this
        monomial.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y
            sage: m = f.lm()
            sage: m.index()
            0

        TESTS:

        Check that :trac:`13133` is resolved::

            sage: B(1).lm().index()
            Traceback (most recent call last):
            ...
            ValueError: no variables in constant monomial ; cannot take index()

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        if self.is_one():
            raise ValueError("no variables in constant monomial ; cannot take index()")
        return (<BooleanPolynomialRing>self.ring()).pbind[self._pbmonom.firstIndex()]

    def deg(BooleanMonomial self):
        """
        Return degree of this monomial.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M(x*y).deg()
            2

            sage: M(x*x*y*z).deg()
            3

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbmonom.deg()

    def degree(BooleanMonomial self, BooleanPolynomial x=None):
        """
        Return the degree of this monomial in ``x``, where
        ``x`` must be one of the generators of the polynomial ring.

        INPUT:

        - ``x`` - boolean multivariate polynomial (a generator of the
          polynomial ring). If ``x`` is not specified (or is ``None``),
          return the total degree of this monomial.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M(x*y).degree()
            2
            sage: M(x*y).degree(x)
            1
            sage: M(x*y).degree(z)
            0
        """
        if not x:
            return self._pbmonom.deg()

        if x not in self._parent.gens():
            raise ValueError("x must be one of the generators of the parent.")

        if self.reducible_by(x.lm()):
            return 1
        else:
            return 0

    def divisors(self):
        """
        Return a set of boolean monomials with all divisors of this
        monomial.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y
            sage: m = f.lm()
            sage: m.divisors()
            {{x,y}, {x}, {y}, {}}
        """
        return new_BS_from_PBSet(self._pbmonom.divisors(), self._ring)

    def multiples(self, BooleanMonomial rhs):
        """
        Return a set of boolean monomials with all multiples of this
        monomial up to the bound ``rhs``.

        INPUT:

        -  ``rhs`` - a boolean monomial

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x
            sage: m = f.lm()
            sage: g = x*y*z
            sage: n = g.lm()
            sage: m.multiples(n)
            {{x,y,z}, {x,y}, {x,z}, {x}}
            sage: n.multiples(m)
            {{x,y,z}}

        .. NOTE::

           The returned set always contains ``self`` even if the bound
           ``rhs`` is smaller than ``self``.
        """
        return new_BS_from_PBSet(self._pbmonom.multiples(rhs._pbmonom),
                self._ring)

    def reducible_by(self, BooleanMonomial rhs):
        """
        Return ``True`` if ``self`` is reducible by ``rhs``.

        INPUT:

        -  ``rhs`` - a boolean monomial

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y
            sage: m = f.lm()
            sage: m.reducible_by((x*y).lm())
            True
            sage: m.reducible_by((x*z).lm())
            False
        """
        return self._pbmonom.reducibleBy(rhs._pbmonom)

    def set(self):
        """
        Return a boolean set of variables in this monomials.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y
            sage: m = f.lm()
            sage: m.set()
            {{x,y}}
        """
        return new_BS_from_PBSet(self._pbmonom.set(), self._ring)

    def __len__(BooleanMonomial self):
        """
        Return 1.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: len(M(x*y))
            1
        """
        return 1

    def __iter__(self):
        """
        Return an iterator over the variables in this monomial.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: list(M(x*z)) # indirect doctest
            [x, z]
        """
        return new_BMVI_from_BooleanMonomial(self)

    def variables(self):
        """
        Return a tuple of the variables in this monomial.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: M(x*z).variables() # indirect doctest
            (x, z)
        """
        return tuple(self)

    def iterindex(self):
        """
        Return an iterator over the indices of the variables in self.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: list(M(x*z).iterindex())
            [0, 2]
        """
        return new_BMI_from_BooleanMonomial(self)

    cpdef _mul_(left, right):
        """
        Multiply this boolean monomial with another boolean monomial.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: x = M(x); xy = M(x*y); z=M(z)
            sage: x*x # indirect doctest
            x

            sage: xy*y
            x*y

            sage: xy*z
            x*y*z
        """
        cdef BooleanMonomial m = new_BM_from_PBMonom(
                (<BooleanMonomial>left)._parent,
                (<BooleanMonomial>left)._ring,
                (<BooleanMonomial>left)._pbmonom)
        m._pbmonom.imul((<BooleanMonomial>right)._pbmonom)
        return m

    def __add__(left, right):
        """
        Addition operator. Return a boolean polynomial.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: x = M(x); xy = M(x*y)
            sage: x + xy
            x*y + x

            sage: x+0
            x
            sage: 0+x   # todo: not implemented
            x

            sage: x+1
            x + 1
            sage: 1 + x     # todo: not implemented
            x + 1
        """
        # Using canonical coercion is not possible for this case.
        # The coercion model cannot find the common parent
        # BooleanPolynomialRing for argument types BooleanMonomial and Integer.
        # This is a common case we should handle as in the examples above.
        # Since we know the result will be a BooleanPolynomial, we let
        # BooleanPolynomial handle the coercion.
        cdef BooleanPolynomial res
        cdef BooleanMonomial monom
        if isinstance(left, BooleanMonomial):
            monom = left
            other = right
        elif isinstance(right, BooleanMonomial):
            monom = right
            other = left
        else:
            raise TypeError("BooleanMonomial.__add__ called with not supported types %s and %s" % (type(right), type(left)))

        res = new_BP_from_PBMonom(monom._ring, monom._pbmonom)
        res += monom._ring._coerce_c(other)
        return res

    def __floordiv__(BooleanMonomial left, right):
        """
        Floordiv operator.

        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: x = M(x); xy = M(x*y)
            sage: xy//x
            y
            sage: x//xy
            0

            sage: x//0
            Traceback (most recent call last):
            ...
            ZeroDivisionError

            sage: x//1
            x
        """
        cdef BooleanMonomial other
        cdef BooleanMonomial m

        if right == 1:
            return left
        elif right == 0:
            raise ZeroDivisionError
        elif not isinstance(right, BooleanMonomial):
            other = left._parent(right)
        else:
            other = <BooleanMonomial>right

        if left._pbmonom.reducibleBy(other._pbmonom):
            m = new_BM_from_PBMonom((<BooleanMonomial>left)._parent,
                                    (<BooleanMonomial>left)._ring,
                                    (<BooleanMonomial>left)._pbmonom)
            m._pbmonom.idiv(other._pbmonom)
            return m
        else:
            return left._ring._zero_element

    def navigation(self):
        """
        Navigators provide an interface to diagram nodes, accessing
        their index as well as the corresponding then- and
        else-branches.

        You should be very careful and always keep a reference to the
        original object, when dealing with navigators, as navigators
        contain only a raw pointer as data. For the same reason, it is
        necessary to supply the ring as argument, when constructing a
        set out of a navigator.

        EXAMPLES::

            sage: from brial import BooleSet
            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3*x4+x2*x4+x3+x4+1
            sage: m = f.lm(); m
            x1*x2

            sage: nav = m.navigation()
            sage: BooleSet(nav, B)
            {{x1,x2}}

            sage: nav.value()
            1
        """
        return self.set().navigation()

    @coerce_binop
    def gcd(self, BooleanMonomial rhs):
        """
        Return the greatest common divisor of this boolean monomial
        and ``rhs``.

        INPUT:

        - ``rhs`` - a boolean monomial


        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: a,b,c,d = a.lm(), b.lm(), c.lm(), d.lm()
            sage: (a*b).gcd(b*c)
            b
            sage: (a*b*c).gcd(d)
            1
        """
        return new_BP_from_PBMonom(self._ring, self._pbmonom.GCD(rhs._pbmonom))

###
#
# Various internal constructors for boolean polynomials from various
# other formats.
#
###

cdef inline BooleanMonomial new_BM(parent, BooleanPolynomialRing ring):
    cdef BooleanMonomial m
    m = <BooleanMonomial>BooleanMonomial.__new__(BooleanMonomial)
    m._parent = parent
    m._ring = ring
    return m

cdef inline BooleanMonomial new_BM_from_PBMonom(parent,
        BooleanPolynomialRing ring, PBMonom juice):
    cdef BooleanMonomial m = new_BM(parent, ring)
    m._pbmonom = juice
    return m

cdef inline BooleanMonomial new_BM_from_PBVar(parent,
        BooleanPolynomialRing ring, PBVar juice):
    cdef BooleanMonomial m = new_BM(parent, ring)
    m._pbmonom = PBMonom(juice)
    return m

cdef class BooleanMonomialVariableIterator:
    def __iter__(self):
        """
        Return an iterator over the variables of a boolean monomial.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y + z + 1
            sage: for m in f: list(m)# indirect doctest
            [x, y]
            [z]
            []
        """
        return self

    def __next__(self):
        """
        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y + z + 1
            sage: m = f.lm()
            sage: next(iter(m))
            x
        """
        cdef PBVar value
        if self._iter == self._end:
            raise StopIteration
        value = self._iter.dereference()
        self._iter.increment()
        return new_BM_from_PBVar(self.parent, self._ring, value)

cdef inline BooleanMonomialVariableIterator new_BMVI_from_BooleanMonomial(
                            BooleanMonomial monom):
    """
    Construct a new iterator over the variable indices of a boolean
    monomial.
    """
    cdef BooleanMonomialVariableIterator m
    m = <BooleanMonomialVariableIterator>BooleanMonomialVariableIterator.__new__(BooleanMonomialVariableIterator)
    m.parent = monom._parent
    m._ring = monom._ring
    m.obj = monom
    m._iter = m.obj._pbmonom.variableBegin()
    m._end  = m.obj._pbmonom.variableEnd()
    return m

cdef class BooleanMonomialIterator:
    """
    An iterator over the variable indices of a monomial.
    """
    def __iter__(self):
        """
        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y + z + 1
            sage: for m in f: list(m.iterindex())# indirect doctest
            [0, 1]
            [2]
            []
        """
        return self

    def __next__(self):
        """
        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y + z + 1
            sage: m = f.lm()
            sage: next(m.iterindex())
            0
        """
        cdef int value
        if self._iter == self._end:
            raise StopIteration
        value = self._iter.dereference()
        self._iter.increment()
        return self.pbind[value]

cdef inline BooleanMonomialIterator new_BMI_from_BooleanMonomial(BooleanMonomial monom):
    """
    Construct a new BooleanMonomialIterator
    """
    cdef BooleanMonomialIterator m
    m = <BooleanMonomialIterator>BooleanMonomialIterator.__new__(BooleanMonomialIterator)
    m._iter = monom._pbmonom.begin()
    m._end  = monom._pbmonom.end()
    m.obj = monom
    m.pbind = (<BooleanPolynomialRing> monom.ring()).pbind
    return m

cdef class BooleanPolynomial(MPolynomial):
    """
    Construct a boolean polynomial object in the given boolean
    polynomial ring.

    INPUT:

    - ``parent`` - a boolean polynomial ring


    TESTS::

        sage: from brial import BooleanPolynomial
        sage: B.<a,b,z> = BooleanPolynomialRing(3)
        sage: BooleanPolynomial(B)
        0

    .. NOTE::

        Do not use this method to construct boolean polynomials, but
        use the appropriate ``__call__`` method in the parent.
    """
    def __init__(self, parent):
        self._parent = parent
        self._pbpoly = PBBoolePolynomial((<BooleanPolynomialRing?>parent)._pbring)

    def _repr_(self):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: repr(a+b+z^2+1) # indirect doctest
            'a + b + z + 1'
        """
        return ccrepr(self._pbpoly)

    def _repr_with_changed_varnames(self, varnames):
        r"""
        Return string representing this boolean polynomial but change the
        variable names to ``varnames``.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: a._repr_with_changed_varnames(['x','y','z'])
            'x'

        TESTS::

            sage: a._repr_with_changed_varnames([1,'y','z'])
            Traceback (most recent call last):
            ...
            TypeError: varnames has entries with wrong type.

        ::

            sage: a
            a
        """
        cdef int i
        cdef BooleanPolynomialRing P = self._parent
        cdef int N = P._pbring.nVariables()

        if len(varnames) != N:
            raise TypeError("len(varnames) doesn't equal self.parent().ngens()")

        orig_varnames = P.variable_names()
        try:
            for i from 0 <= i < N:
                P._pbring.setVariableName(i, str_to_bytes(varnames[i]))
        except TypeError:
            for i from 0 <= i < N:
                P._pbring.setVariableName(i, str_to_bytes(orig_varnames[i]))
            raise TypeError("varnames has entries with wrong type.")
        s = ccrepr(self._pbpoly)
        for i from 0 <= i < N:
            P._pbring.setVariableName(i, str_to_bytes(orig_varnames[i]))
        return s

    def _latex_(self):
        r"""
        Return a LaTeX representation of this boolean polynomial.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: latex(a+b+a*z^2+1) # indirect doctest
            a z + a + b + 1
        """
        R = self.parent().cover_ring()
        return R(self)._latex_()

    cpdef _add_(left, right):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*z + b + 1
            sage: g = b + z
            sage: f + g # indirect doctest
            a*z + z + 1
        """
        cdef BooleanPolynomial p = new_BP_from_PBPoly(
                (<BooleanPolynomial>left)._parent, (<BooleanPolynomial>left)._pbpoly)
        p._pbpoly.iadd((<BooleanPolynomial>right)._pbpoly)
        return p

    cpdef _sub_(left, right):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*z + b + 1
            sage: g = b + z
            sage: f - g  # indirect doctest
            a*z + z + 1
        """
        return left._add_(right)

    cpdef _lmul_(self, Element left):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: k = B.base_ring()
            sage: f = a*z + b + 1
            sage: f*k(1)  # indirect doctest
            a*z + b + 1

        ::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: k = B.base_ring()
            sage: f = a*z + b + 1
            sage: k(0)*f # indirect doctest
            0
        """
        if left:
            return new_BP_from_PBPoly(self._parent, self._pbpoly)
        else:
            return self._parent.zero()

    cpdef _mul_(left, right):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*z + b + 1
            sage: g = b + z
            sage: f * g # indirect doctest
            a*b*z + a*z + b*z + z
        """
        cdef BooleanPolynomial p = new_BP_from_PBPoly(
                (<BooleanPolynomial>left)._parent, (<BooleanPolynomial>left)._pbpoly)
        p._pbpoly.imul((<BooleanPolynomial>right)._pbpoly)
        return p

    cpdef _div_(left, right):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*z + b + 1
            sage: f / a
            z
            sage: f = z + b + 1
            sage: f / a
            0
        """
        cdef BooleanPolynomial p = new_BP_from_PBPoly(
                (<BooleanPolynomial>left)._parent, (<BooleanPolynomial>left)._pbpoly)
        p._pbpoly.idiv((<BooleanPolynomial>right)._pbpoly)
        return p

    def is_equal(self, BooleanPolynomial right):
        """
        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*z + b + 1
            sage: g = b + z
            sage: f.is_equal(g)
            False

        ::

            sage: f.is_equal((f + 1) - 1)
            True

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly == right._pbpoly

    cpdef _richcmp_(left, right, int op):
        """
        Compare left and right.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: x < x+y
            True

            sage: y*z < x
            True

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: y*z < x
            False
            sage: P(True) == True
            True
            sage: P(0) == 0
            True

        TESTS::

            sage: P.<x> = BooleanPolynomialRing()
            sage: P(True) == True
            True
            sage: P.zero() == True
            False
            sage: P(0) != True
            True
            sage: P(False) == False
            True
            sage: P() != False
            False
            sage: x == True
            False
            sage: x != True
            True
            sage: x == False
            False
            sage: x != False
            True
        """
        for lm, rm in zip(left, right):
            if lm != rm:
                return richcmp_not_equal(lm, rm, op)

        return richcmp(len(left), len(right), op)

    def __iter__(self):
        r"""
        Return an iterator over the monomials of ``self``, in
        the order of the parent ring.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: p = x + z + x*y + y*z + x*y*z
            sage: list(iter(p))
            [x*y*z, x*y, x, y*z, z]

        ::

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: p = x + z + x*y + y*z + x*y*z
            sage: list(iter(p))
            [x*y*z, x*y, y*z, x, z]

        ::

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: p = x + z + x*y + y*z + x*y*z
            sage: list(iter(p))
            [x*y*z, x*y, y*z, x, z]

        TESTS::

            sage: R = BooleanPolynomialRing(1,'y')
            sage: list(iter(y))
            [y]
            sage: R
            Boolean PolynomialRing in y
        """
        return new_BPI_from_BooleanPolynomial(self)

    def __pow__(BooleanPolynomial self, int exp, ignored):
        r"""
        Return ``self^(exp)``.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: p = x + y
            sage: p^0
            1

        ::

            sage: p^1
            x + y

        ::

            sage: p^5
            x + y

        ::

            sage: p^-1
            Traceback (most recent call last):
            ...
            NotImplementedError: Negative exponents for non constant boolean polynomials not implemented.

        ::

            sage: z = P(0)
            sage: z^0
            1

        ::

            sage: z^1
            0
        """
        if exp > 0:
            return self
        elif exp == 0:
            return self._parent._one_element
        elif self._pbpoly.isOne():
            return self
        elif self._pbpoly.isZero():
            raise ZeroDivisionError
        else:
            raise NotImplementedError("Negative exponents for non constant boolean polynomials not implemented.")

    def __neg__(BooleanPolynomial self):
        r"""
        Return -``self``.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*z + b + 1
            sage: -f
            a*z + b + 1
        """
        return self

    def total_degree(BooleanPolynomial self):
        r"""
        Return the total degree of ``self``.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: (x+y).total_degree()
            1

        ::

            sage: P(1).total_degree()
            0

        ::

            sage: (x*y + x + y + 1).total_degree()
            2
        """
        return self._pbpoly.deg()

    def degree(self, BooleanPolynomial x=None):
        r"""
        Return the maximal degree of this polynomial in ``x``, where
        ``x`` must be one of the generators for the parent of this
        polynomial.

        If x is not specified (or is ``None``), return the total
        degree, which is the maximum degree of any monomial.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: (x+y).degree()
            1

        ::

            sage: P(1).degree()
            0

        ::

            sage: (x*y + x + y + 1).degree()
            2

            sage: (x*y + x + y + 1).degree(x)
            1
        """
        if x is not None:
            if self._pbpoly.set().multiplesOf(x._pbpoly.firstTerm()).isZero():
                return 0
            else:
                return 1
        return self._pbpoly.deg()

    def lm(BooleanPolynomial self):
        r"""
        Return the leading monomial of this boolean polynomial, with
        respect to the order of parent ring.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: (x+y+y*z).lm()
            x

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: (x+y+y*z).lm()
            y*z

            sage: P(0).lm()
            0
        """
        if self._pbpoly.isZero():
            return self._parent._zero_element
        return new_BM_from_PBMonom(self._parent._monom_monoid, self._parent,
                self._pbpoly.lead())

    def lt(BooleanPolynomial self):
        """
        Return the leading term of this boolean polynomial, with respect to
        the order of the parent ring.

        Note that for boolean polynomials this is equivalent to returning
        leading monomials.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: (x+y+y*z).lt()
            x

        ::

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: (x+y+y*z).lt()
            y*z
        """
        return self.lm()

    def is_singleton(BooleanPolynomial self):
        r"""
        Check if ``self`` has at most one term.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(0).is_singleton()
            True

        ::

            sage: x.is_singleton()
            True

        ::

            sage: P(1).is_singleton()
            True

        ::

            sage: (x*y).is_singleton()
            True

        ::

            sage: (x + y).is_singleton()
            False

        ::

            sage: (x + 1).is_singleton()
            False

        ::

            sage: (x*y + 1).is_singleton()
            False

        ::

            sage: (x + y + 1).is_singleton()
            False

        ::

            sage: ((x + 1)*(y + 1)).is_singleton()
            False

        """
        return self._pbpoly.isSingleton()

    def is_singleton_or_pair(BooleanPolynomial self):
        r"""
        Check if ``self`` has at most two terms.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(0).is_singleton_or_pair()
            True

        ::

            sage: x.is_singleton_or_pair()
            True

        ::

            sage: P(1).is_singleton_or_pair()
            True

        ::

            sage: (x*y).is_singleton_or_pair()
            True

        ::

            sage: (x + y).is_singleton_or_pair()
            True

        ::

            sage: (x + 1).is_singleton_or_pair()
            True

        ::

            sage: (x*y + 1).is_singleton_or_pair()
            True

        ::

            sage: (x + y + 1).is_singleton_or_pair()
            False

        ::

            sage: ((x + 1)*(y + 1)).is_singleton_or_pair()
            False

        """
        return self._pbpoly.isSingletonOrPair()

    def is_pair(BooleanPolynomial self):
        r"""
        Check if ``self`` has exactly two terms.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(0).is_singleton_or_pair()
            True

        ::

            sage: x.is_singleton_or_pair()
            True

        ::

            sage: P(1).is_singleton_or_pair()
            True

        ::

            sage: (x*y).is_singleton_or_pair()
            True

        ::

            sage: (x + y).is_singleton_or_pair()
            True

        ::

            sage: (x + 1).is_singleton_or_pair()
            True

        ::

            sage: (x*y + 1).is_singleton_or_pair()
            True

        ::

            sage: (x + y + 1).is_singleton_or_pair()
            False

        ::

            sage: ((x + 1)*(y + 1)).is_singleton_or_pair()
            False

        """
        return self._pbpoly.isPair()

    def is_zero(BooleanPolynomial self):
        r"""
        Check if ``self`` is zero.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(0).is_zero()
            True

        ::

            sage: x.is_zero()
            False

        ::

            sage: P(1).is_zero()
            False
        """
        return self._pbpoly.isZero()

    def __nonzero__(self):
        r"""
        Check if ``self`` is zero.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: bool(P(0))
            False

        ::

            sage: bool(x)
            True

        ::

            sage: bool(P(1))
            True
        """
        return not self._pbpoly.isZero()

    def is_one(BooleanPolynomial self):
        """
        Check if self is 1.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(1).is_one()
            True

        ::

            sage: P.one().is_one()
            True

        ::

            sage: x.is_one()
            False

        ::

            sage: P(0).is_one()
            False
        """
        return self._pbpoly.isOne()

    def is_unit(BooleanPolynomial self):
        r"""
        Check if ``self`` is invertible in the parent ring.

        Note that this condition is equivalent to being 1 for boolean
        polynomials.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P.one().is_unit()
            True

        ::

            sage: x.is_unit()
            False
        """
        return self._pbpoly.isOne()

    def is_constant(BooleanPolynomial self):
        r"""
        Check if ``self`` is constant.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: P(1).is_constant()
            True

        ::

            sage: P(0).is_constant()
            True

        ::

            sage: x.is_constant()
            False

        ::

            sage: (x*y).is_constant()
            False
        """
        return self._pbpoly.isConstant()

    def lead_deg(BooleanPolynomial self):
        r"""
        Return the total degree of the leading monomial of
        ``self``.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: p = x + y*z
            sage: p.lead_deg()
            1

        ::

            sage: P.<x,y,z> = BooleanPolynomialRing(3,order='deglex')
            sage: p = x + y*z
            sage: p.lead_deg()
            2

        ::

            sage: P(0).lead_deg()
            0

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        if self._pbpoly.isZero():
            return 0
        return self._pbpoly.leadDeg()

    def vars_as_monomial(self):
        r"""
        Return a boolean monomial with all the variables appearing in
        ``self``.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: (x + y).vars_as_monomial()
            x*y

        ::

            sage: (x*y + z).vars_as_monomial()
            x*y*z

        ::

            sage: P.zero().vars_as_monomial()
            1

        ::

            sage: P.one().vars_as_monomial()
            1

        TESTS::

            sage: R = BooleanPolynomialRing(1, 'y')
            sage: y.vars_as_monomial()
            y
            sage: R
            Boolean PolynomialRing in y

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return new_BM_from_PBMonom(self._parent._monom_monoid,
                self._parent, self._pbpoly.usedVariables())

    def variables(self):
        r"""
        Return a tuple of all variables appearing in ``self``.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: (x + y).variables()
            (x, y)

        ::

            sage: (x*y + z).variables()
            (x, y, z)

        ::

            sage: P.zero().variables()
            ()

        ::

            sage: P.one().variables()
            ()
        """
        P = self.parent()
        o = P.one()
        if self is o or self == o:
            return tuple()
        return tuple(self.vars_as_monomial())

    def nvariables(self):
        """
        Return the number of variables used to form this boolean
        polynomial.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: f = a*b*c + 1
            sage: f.nvariables()
            3
        """
        return self._pbpoly.nUsedVariables()

    def is_univariate(self):
        """
        Return ``True`` if self is a univariate polynomial, that is if
        self contains only one variable.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing()
            sage: f = x + 1
            sage: f.is_univariate()
            True
            sage: f = y*x + 1
            sage: f.is_univariate()
            False
            sage: f = P(0)
            sage: f.is_univariate()
            True
        """
        return self.nvariables() <= 1

    def univariate_polynomial(self, R=None):
        """
        Return a univariate polynomial associated to this
        multivariate polynomial.

        If this polynomial is not in at most one variable, then a
        ``ValueError`` exception is raised.  This is checked using the
        :meth:`is_univariate()` method.  The new Polynomial is over
        GF(2)  and in the variable ``x`` if no ring ``R`` is provided.

            sage: R.<x, y> = BooleanPolynomialRing()
            sage: f = x - y + x*y + 1
            sage: f.univariate_polynomial()
            Traceback (most recent call last):
            ...
            ValueError: polynomial must involve at most one variable
            sage: g = f.subs({x:0}); g
            y + 1
            sage: g.univariate_polynomial ()
            y + 1
            sage: g.univariate_polynomial(GF(2)['foo'])
            foo + 1

        Here's an example with a constant multivariate polynomial::

            sage: g = R(1)
            sage: h = g.univariate_polynomial(); h
            1
            sage: h.parent()
            Univariate Polynomial Ring in x over Finite Field of size 2 (using GF2X)
        """
        if not self.is_univariate():
            raise ValueError("polynomial must involve at most one variable")

        #construct ring if none
        if R is None:
            if self.is_constant():
                R = GF(2)['x']
            else:
                R = GF(2)[str(self.variable(0))]

        coefficients = [0, 0]
        for m in self.monomials():
            coefficients[m.degree()] = 1

        return R(coefficients)

    def monomials(self):
        r"""
        Return a list of monomials appearing in ``self``
        ordered largest to smallest.

        EXAMPLES::

            sage: P.<a,b,c> = BooleanPolynomialRing(3,order='lex')
            sage: f = a + c*b
            sage: f.monomials()
            [a, b*c]

        ::

            sage: P.<a,b,c> = BooleanPolynomialRing(3,order='deglex')
            sage: f = a + c*b
            sage: f.monomials()
            [b*c, a]
            sage: P.zero().monomials()
            []
        """
        return list(self)

    def variable(self, i=0):
        """
        Return the i-th variable occurring in self. The index i is the
        index in ``self.variables()``

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*z + z + 1
            sage: f.variables()
            (x, z)
            sage: f.variable(1)
            z
        """
        return self.variables()[i]

    def terms(self):
        """
        Return a list of monomials appearing in ``self`` ordered
        largest to smallest.

        EXAMPLES::

            sage: P.<a,b,c> = BooleanPolynomialRing(3,order='lex')
            sage: f = a + c*b
            sage: f.terms()
            [a, b*c]

            sage: P.<a,b,c> = BooleanPolynomialRing(3,order='deglex')
            sage: f = a + c*b
            sage: f.terms()
            [b*c, a]
        """
        return list(self)

    def monomial_coefficient(self, mon):
        r"""
        Return the coefficient of the monomial ``mon`` in
        ``self``, where ``mon`` must have the same
        parent as ``self``.

        INPUT:


        -  ``mon`` - a monomial


        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: x.monomial_coefficient(x)
            1
            sage: x.monomial_coefficient(y)
            0
            sage: R.<x,y,z,a,b,c>=BooleanPolynomialRing(6)
            sage: f=(1-x)*(1+y); f
            x*y + x + y + 1

        ::

            sage: f.monomial_coefficient(1)
            1

        ::

            sage: f.monomial_coefficient(0)
            0
        """
        cdef BooleanPolynomialRing B = <BooleanPolynomialRing>self._parent
        k = B._base
        mon = B._coerce_c(mon)
        if mon in set(self.set()):
            return k._one_element
        else:
            return k._zero_element

    def constant_coefficient(self):
        """
        Return the constant coefficient of this boolean polynomial.

        EXAMPLES::

            sage: B.<a,b> = BooleanPolynomialRing()
            sage: a.constant_coefficient()
            0
            sage: (a+1).constant_coefficient()
            1
        """
        cdef BooleanPolynomialRing B = <BooleanPolynomialRing>self._parent
        if self._pbpoly.hasConstantPart():
            return B._base._one_element
        else:
            return B._base._zero_element

    def __hash__(self):
        r"""
        Return hash for ``self``.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: {x:1} # indirect doctest
            {x: 1}
        """
        return <Py_ssize_t>(self._pbpoly.stableHash())

    def __len__(self):
        r"""
        Return number of monomials in ``self``.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: len(x + y)
            2

        ::

            sage: len(P.one())
            1

        ::

            sage: len(x*y + y + z + x*z)
            4

        ::

            sage: len(P.zero())
            0
        """
        return self._pbpoly.length()

    def __call__(self, *args, **kwds):
        """
        Evaluate this boolean polynomials.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y + z + 1
            sage: f(0,1,1)
            0
            sage: f(z,y,x)
            x + y*z + 1
            sage: f(x=z)
            y*z + z + 1

        ::

            sage: P.<a,b,c> = PolynomialRing(QQ)
            sage: f(a,b,c)
            a*b + c + 1
            sage: f(x=a,y=b,z=1)
            a*b + 2

        Evaluation of polynomials can be used fully symbolic::

            sage: f(x=var('a'),y=var('b'),z=var('c'))
            a*b + c + 1
            sage: f(var('a'),var('b'),1)
            a*b
        """
        P = self._parent
        cdef int N = P.ngens()
        if args and kwds:
            raise ValueError("Using keywords and regular arguments not supported.")
        if args:
            d = {}
            if len(args) != N:
                raise ValueError("Number of arguments is different from the number of variables of parent ring.")
            for i in range(N):
                arg = args[i]
                try:
                    arg = P.coerce(arg)
                    if arg.constant():
                        # TODO: We should collect those and reduce once only
                        self = ll_red_nf_redsb(self, (P.gen(i) + arg).set())
                    else:
                        d[i] = arg
                except TypeError:
                    d[i] = arg
            if not len(d):
                return self
        elif kwds:
            d = dict(zip(range(P.ngens()), P.gens()))
            gd = dict(zip(P.variable_names(),range(P.ngens())))
            for var,val in kwds.iteritems():
                d[gd[var]] = val

        res = 0
        for m in self:
            res += m._eval(d)
        return res

    def subs(self, in_dict=None, **kwds):
        r"""
        Fixes some given variables in a given boolean polynomial and
        returns the changed boolean polynomials. The polynomial itself is
        not affected. The variable,value pairs for fixing are to be
        provided as dictionary of the form {variable:value} or named
        parameters (see examples below).

        INPUT:


        -  ``in_dict`` - (optional) dict with variable:value
           pairs

        -  ``**kwds`` - names parameters


        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: f = x*y + z + y*z + 1
            sage: f.subs(x=1)
            y*z + y + z + 1
            sage: f.subs(x=0)
            y*z + z + 1

        ::

            sage: f.subs(x=y)
            y*z + y + z + 1

        ::

            sage: f.subs({x:1},y=1)
            0
            sage: f.subs(y=1)
            x + 1
            sage: f.subs(y=1,z=1)
            x + 1
            sage: f.subs(z=1)
            x*y + y
            sage: f.subs({'x':1},y=1)
            0

        This method can work fully symbolic::

            sage: f.subs(x=var('a'),y=var('b'),z=var('c'))
            a*b + b*c + c + 1
            sage: f.subs({'x':var('a'),'y':var('b'),'z':var('c')})
            a*b + b*c + c + 1
        """
        P = self._parent

        fixed = {}
        if in_dict is not None:
            for var,val in in_dict.items():
                if isinstance(var, basestring):
                    var = P(var)
                elif var.parent() is not P:
                    var = P(var)
                try:
                    v = P(val)
                    if v.constant():
                        self = ll_red_nf_redsb(self, (var + v).set())
                    else:
                        fixed[var.lm().index()] = val
                except TypeError:
                    fixed[var.lm().index()] = val
        if kwds:
            gdict = P._monom_monoid.gens_dict()

        for var,val in kwds.iteritems():
            var = gdict[var]
            try:
                v = P(val)
                if v.constant():
                    self = ll_red_nf_redsb(self, (var + v).set())
                else:
                    fixed[var.index()] = val
            except TypeError:
                fixed[var.index()] = val

        if not len(fixed):
            return self
        res = 0
        for m in self:
            res += m._eval(fixed)
        return res

    def __reduce__(self):
        """
        EXAMPLES::

            sage: P.<a,b> = BooleanPolynomialRing(2)
            sage: loads(dumps(a)) == a
            True
        """
        from brial.parallel import _encode_polynomial
        return unpickle_BooleanPolynomial0, (self._parent,
                                             _encode_polynomial(self))

    def _magma_init_(self, magma):
        r"""
        Return the Magma representation of self.

        EXAMPLES::

            sage: R.<x,y> = BooleanPolynomialRing()
            sage: f = y*x + x +1
            sage: f._magma_init_(magma)               # optional - magma
            '_sage_[...]*_sage_[...] + _sage_[...] + 1'
            sage: magma(f)                            # optional - magma
            x*y + x + 1
        """
        magma_gens = [e.name() for e in magma(self.parent()).gens()]
        return self._repr_with_changed_varnames(magma_gens)

    def is_homogeneous(self):
        r"""
        Return ``True`` if this element is a homogeneous
        polynomial.

        EXAMPLES::

            sage: P.<x, y> = BooleanPolynomialRing()
            sage: (x+y).is_homogeneous()
            True
            sage: P(0).is_homogeneous()
            True
            sage: (x+1).is_homogeneous()
            False
        """
        M = self.set()
        try: # 0
            d = next(iter(M)).degree()
        except StopIteration:
            return True
        for m in M:
            if m.degree() != d:
                return False
        return True

    def set(self):
        r"""
        Return a ``BooleSet`` with all monomials appearing in
        this polynomial.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: (a*b+z+1).set()
            {{a,b}, {z}, {}}
        """
        return new_BS_from_PBSet(self._pbpoly.set(), self._parent)

    def deg(self):
        r"""
        Return the degree of ``self``. This is usually
        equivalent to the total degree except for weighted term orderings
        which are not implemented yet.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: (x+y).degree()
            1

        ::

            sage: P(1).degree()
            0

        ::

            sage: (x*y + x + y + 1).degree()
            2

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.deg()

    def elength(self):
        r"""
        Return elimination length as used in the SlimGB algorithm.

        EXAMPLES::

            sage: P.<x,y> = BooleanPolynomialRing(2)
            sage: x.elength()
            1
            sage: f = x*y + 1
            sage: f.elength()
            2

        REFERENCES:

        - Michael Brickenstein; SlimGB: Groebner Bases with Slim
          Polynomials
          http://www.mathematik.uni-kl.de/~zca/Reports_on_ca/35/paper_35_full.ps.gz

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.eliminationLength()

    def lead(self):
        r"""
        Return the leading monomial of boolean polynomial, with respect to
        to the order of parent ring.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: (x+y+y*z).lead()
            x

        ::

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: (x+y+y*z).lead()
            y*z

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return new_BM_from_PBMonom(self._parent._monom_monoid, self._parent,
                                   self._pbpoly.lead())

    def lex_lead(self):
        r"""
        Return the leading monomial of boolean polynomial, with respect to
        the lexicographical term ordering.

        EXAMPLES::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: (x+y+y*z).lex_lead()
            x

            sage: P.<x,y,z> = BooleanPolynomialRing(3, order='deglex')
            sage: (x+y+y*z).lex_lead()
            x

            sage: P(0).lex_lead()
            0

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        if self._pbpoly.isZero():
            return self._parent._zero_element

        return new_BM_from_PBMonom(self._parent._monom_monoid, self._parent,
                                                self._pbpoly.lexLead())

    def lex_lead_deg(self):
        """
        Return degree of leading monomial with respect to the
        lexicographical ordering.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3,order='lex')
            sage: f = x + y*z
            sage: f
            x + y*z
            sage: f.lex_lead_deg()
            1

        ::

            sage: B.<x,y,z> = BooleanPolynomialRing(3,order='deglex')
            sage: f = x + y*z
            sage: f
            y*z + x
            sage: f.lex_lead_deg()
            1

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.lexLeadDeg()

    def constant(self):
        r"""
        Return ``True`` if this element is constant.

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(3)
            sage: x.constant()
            False

        ::

            sage: B(1).constant()
            True

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.isConstant()

    def navigation(self):
        """
        Navigators provide an interface to diagram nodes, accessing
        their index as well as the corresponding then- and
        else-branches.

        You should be very careful and always keep a reference to the
        original object, when dealing with navigators, as navigators
        contain only a raw pointer as data. For the same reason, it is
        necessary to supply the ring as argument, when constructing a
        set out of a navigator.

        EXAMPLES::

            sage: from brial import BooleSet
            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3*x4+x2*x4+x3+x4+1

            sage: nav = f.navigation()
            sage: BooleSet(nav, B)
            {{x1,x2}, {x2,x3,x4}, {x2,x4}, {x3}, {x4}, {}}

            sage: nav.value()
            1

            sage: nav_else = nav.else_branch()

            sage: BooleSet(nav_else, B)
            {{x2,x3,x4}, {x2,x4}, {x3}, {x4}, {}}

            sage: nav_else.value()
            2

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return new_CN_from_PBNavigator(self._pbpoly.navigation(),
                                       (<BooleanPolynomialRing>self._parent).pbind)

    def map_every_x_to_x_plus_one(self):
        """
        Map every variable ``x_i`` in this polynomial to ``x_i + 1``.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*b + z + 1; f
            a*b + z + 1
            sage: f.map_every_x_to_x_plus_one()
            a*b + a + b + z + 1
            sage: f(a+1,b+1,z+1)
            a*b + a + b + z + 1

        """
        return new_BP_from_PBPoly(self._parent,
                pb_map_every_x_to_x_plus_one(self._pbpoly))

    def lead_divisors(self):
        r"""
        Return a ``BooleSet`` of all divisors of the leading
        monomial.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3)
            sage: f = a*b + z + 1
            sage: f.lead_divisors()
            {{a,b}, {a}, {b}, {}}

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return new_BS_from_PBSet(self._pbpoly.leadDivisors(), self._parent)

    def first_term(self):
        r"""
        Return the first term with respect to the lexicographical term
        ordering.

        EXAMPLES::

            sage: B.<a,b,z> = BooleanPolynomialRing(3,order='lex')
            sage: f = b*z + a + 1
            sage: f.first_term()
            a

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return new_BM_from_PBMonom(self._parent._monom_monoid, self._parent,
                self._pbpoly.firstTerm())

    def reducible_by(self, BooleanPolynomial rhs):
        r"""
        Return ``True`` if this boolean polynomial is reducible
        by the polynomial ``rhs``.

        INPUT:


        -  ``rhs`` - a boolean polynomial


        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4,order='deglex')
            sage: f = (a*b + 1)*(c + 1)
            sage: f.reducible_by(d)
            False
            sage: f.reducible_by(c)
            True
            sage: f.reducible_by(c + 1)
            True

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.firstReducibleBy(rhs._pbpoly)

    def n_nodes(self):
        """
        Return the number of nodes in the ZDD implementing this
        polynomial.

        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2 + x2*x3 + 1
            sage: f.n_nodes()
            4

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.nNodes()

    def n_vars(self):
        """
        Return the number of variables used to form this boolean
        polynomial.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: f = a*b*c + 1
            sage: f.n_vars()
            3

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return self._pbpoly.nUsedVariables()

    def graded_part(self, int deg):
        r"""
        Return graded part of this boolean polynomial of degree
        ``deg``.

        INPUT:


        -  ``deg`` - a degree


        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: f = a*b*c + c*d + a*b + 1
            sage: f.graded_part(2)
            a*b + c*d

        ::

            sage: f.graded_part(0)
            1

        TESTS::

            sage: f.graded_part(-1)
            0
        """
        return new_BP_from_PBPoly(self._parent,
                self._pbpoly.gradedPart(deg))

    def has_constant_part(self):
        r"""
        Return ``True`` if this boolean polynomial has a
        constant part, i.e. if ``1`` is a term.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: f = a*b*c + c*d + a*b + 1
            sage: f.has_constant_part()
            True

        ::

            sage: f = a*b*c + c*d + a*b
            sage: f.has_constant_part()
            False
        """
        return self._pbpoly.hasConstantPart()

    def zeros_in(self, s):
        r"""
        Return a set containing all elements of ``s`` where
        this boolean polynomial evaluates to zero.

        If ``s`` is given as a ``BooleSet``, then
        the return type is also a ``BooleSet``. If
        ``s`` is a set/list/tuple of tuple this function
        returns a tuple of tuples.

        INPUT:


        -  ``s`` - candidate points for evaluation to zero


        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: f = a*b + c + d + 1

        Now we create a set of points::

            sage: s = a*b + a*b*c + c*d + 1
            sage: s = s.set(); s
            {{a,b,c}, {a,b}, {c,d}, {}}

        This encodes the points (1,1,1,0), (1,1,0,0), (0,0,1,1) and
        (0,0,0,0). But of these only (1,1,0,0) evaluates to zero.

        ::

            sage: f.zeros_in(s)
            {{a,b}}

        ::

            sage: f.zeros_in([(1,1,1,0), (1,1,0,0), (0,0,1,1), (0,0,0,0)])
            ((1, 1, 0, 0),)
        """
        if isinstance(s, BooleSet):
            return new_BS_from_PBSet(pb_zeros(self._pbpoly, (<BooleSet>s)._pbset), self._parent)
        elif isinstance(s, (list, tuple, set)):
            from sage.misc.misc_c import prod
            B = self.parent()
            n = B.ngens()
            x = B.gens()
            one = B.one()
            zero = B.zero()
            s = sum([prod([x[i] for i in reversed(range(n)) if v[i]], one)
                     for v in s], zero)
            s = s.set()
            r = new_BS_from_PBSet(pb_zeros(self._pbpoly, (<BooleSet>s)._pbset), self._parent)
            L= []
            for e in r:
                l = [0] * n
                for i in e.iterindex():
                    l[i] = 1
                L.append(tuple(l))
            return tuple(L)
        else:
            raise TypeError("Type '%s' of s not supported." % type(s))

    def spoly(self, BooleanPolynomial rhs):
        r"""
        Return the S-Polynomial of this boolean polynomial and the other
        boolean polynomial ``rhs``.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: f = a*b*c + c*d + a*b + 1
            sage: g = c*d + b
            sage: f.spoly(g)
            a*b + a*c*d + c*d + 1

        .. NOTE::

           This function is part of the upstream PolyBoRi interface.
        """
        return new_BP_from_PBPoly(self._parent,
                pb_spoly(self._pbpoly, rhs._pbpoly))

    def stable_hash(self):
        """
        A hash value which is stable across processes.

        EXAMPLES::

            sage: B.<x,y> = BooleanPolynomialRing()
            sage: x is B.gen(0)
            False
            sage: x.stable_hash() == B.gen(0).stable_hash()
            True

        .. NOTE::

           This function is part of the upstream PolyBoRi
           interface. In Sage all hashes are stable.
        """
        return <Py_ssize_t>(self._pbpoly.stableHash())

    def ring(self):
        """
        Return the parent of this boolean polynomial.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: a.ring() is B
            True
        """
        return self._parent

    def reduce(self, I):
        r"""
        Return the normal form of ``self`` w.r.t.  ``I``, i.e. return
        the remainder of ``self`` with respect to the polynomials in
        ``I``. If the polynomial set/list ``I`` is not a Groebner
        basis the result is not canonical.

        INPUT:


        -  ``I`` - a list/set of polynomials in self.parent().
           If I is an ideal, the generators are used.


        EXAMPLES::

            sage: B.<x0,x1,x2,x3> = BooleanPolynomialRing(4)
            sage: I = B.ideal((x0 + x1 + x2 + x3,
            ....:              x0*x1 + x1*x2 + x0*x3 + x2*x3,
            ....:              x0*x1*x2 + x0*x1*x3 + x0*x2*x3 + x1*x2*x3,
            ....:              x0*x1*x2*x3 + 1))
            sage: gb = I.groebner_basis()
            sage: f,g,h,i = I.gens()
            sage: f.reduce(gb)
            0
            sage: p = f*g + x0*h + x2*i
            sage: p.reduce(gb)
            0
            sage: p.reduce(I)
            x1*x2*x3 + x2
            sage: p.reduce([])
            x0*x1*x2 + x0*x1*x3 + x0*x2*x3 + x2

        .. NOTE::

           If this function is called repeatedly with the same I then
           it is advised to use PolyBoRi's :class:`GroebnerStrategy`
           object directly, since that will be faster. See the source
           code of this function for details.

        TESTS::

            sage: R=BooleanPolynomialRing(20,'x','lex')
            sage: a=R.random_element()
            sage: a.reduce([None,None])
            Traceback (most recent call last):
            ...
            TypeError: argument must be a BooleanPolynomial.
        """
        from brial import red_tail
        if not I:
            return self
        if isinstance(I, BooleanPolynomialIdeal):
            I = I.gens()
        first = I[0]
        if first is None:
            raise TypeError("argument must be a BooleanPolynomial.")
        g = ReductionStrategy(first.ring())
        g.opt_red_tail = True
        for p in I:
            g.add_generator(p)
        return g.nf(self)


cdef class PolynomialConstruct:
    """
    Implements PolyBoRi's ``Polynomial()`` constructor.
    """
    def lead(self, x):
        """
        Return the leading monomial of boolean polynomial ``x``, with
        respect to the order of parent ring.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: PolynomialConstruct().lead(a)
            a
        """
        return x.lead()

    def __call__(self, x, ring=None):
        """
        Construct a new :class:`BooleanPolynomial` or return ``x`` if
        it is a :class:`BooleanPolynomial` already.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: PolynomialConstruct()(1, B)
            1
            sage: PolynomialConstruct()(a)
            a
        """
        if isinstance(x, BooleanPolynomial):
            return x
        elif isinstance(x, BooleSet):
            return (<BooleSet>x)._ring._element_constructor_(x)
        elif isinstance(x, BooleanMonomial):
            return (<BooleanMonomial>x)._ring(x)
        elif isinstance(ring, BooleanPolynomialRing):
            # It is a wrong use of the notion of "coercion"
            # to say that the boolean set is "coerced" into
            # a boolean polynomial ring: Boolean sets have
            # no parent, and thus there is no coercion map
            # from that parent to the ring.
            # So, it is just a conversion. [Simon King]
            return (<BooleanPolynomialRing>ring)._element_constructor_(x)

        raise TypeError("Cannot generate Boolean polynomial from %s , %s" %
                        (type(x), type(ring)))


cdef class MonomialConstruct:
    """
    Implements PolyBoRi's ``Monomial()`` constructor.
    """
    def __call__(self, x):
        """
        Construct a new :class:`BooleanMonomial` or return ``x`` if
        it is a :class:`BooleanMonomial` already.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: MonomialConstruct()(B)
            1
            sage: MonomialConstruct()(a.lm())
            a
            sage: MonomialConstruct()(a)
            a
        """
        if isinstance(x, BooleanMonomial):
            return x
        elif isinstance(x, BooleanPolynomialRing):
            return (<BooleanPolynomialRing>x)._monom_monoid._one_element
        elif isinstance(x, BooleanPolynomial) and x.is_singleton():
            return (<BooleanPolynomial>x).lm()
        else:
            try:
                result = x[-1]
                for elt in reversed(x[:-1]):
                    result = result * elt
                if isinstance(x, BooleanPolynomial):
                    return result.lm()
                return result
            except Exception:
                raise TypeError("Cannot convert to Boolean Monomial %s" %
                                type(x))

cdef class VariableConstruct:
    """
    Implements PolyBoRi's ``Variable()`` constructor.
    """
    def __call__(self, arg, ring=None):
        """
        Return a Variable for ``x``.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: VariableConstruct()(B)
            a
            sage: VariableConstruct()(0, B)
            a
        """
        if isinstance(arg, BooleanPolynomialRing):
            return arg.variable(0)
        elif isinstance(ring, BooleanPolynomialRing):
            return (<BooleanPolynomialRing>ring).variable(arg)
        else:
            raise TypeError("todo polynomial factory %s%s" %
                            (str(type(arg)),str(type(ring))))


cdef class BooleanPolynomialIterator:
    """
    Iterator over the monomials of a boolean polynomial.
    """
    def __dealloc__(self):
        del self._iter
        del self._end

    def __iter__(self):
        """
        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: list(B.random_element()) # indirect doctest
            [a*b, a*c, a, b*d, 1]
        """
        return self

    def __next__(self):
        """
        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: it = iter(B.random_element())
            sage: next(it) # indirect doctest
            a*b
        """
        cdef PBMonom value
        if deref(self._iter) == deref(self._end):
            raise StopIteration
        value = self._iter.dereference()
        self._iter.increment()
        return new_BM_from_PBMonom(self.obj._parent._monom_monoid,
                self.obj._parent, value)


cdef inline BooleanPolynomialIterator new_BPI_from_BooleanPolynomial(BooleanPolynomial f):
    """
    Construct a new BooleanMonomialIterator
    """
    cdef BooleanPolynomialIterator m
    m = <BooleanPolynomialIterator>BooleanPolynomialIterator.__new__(BooleanPolynomialIterator)
    m.obj = f
    m._iter = new PBPolyIter(f._pbpoly.orderedBegin())
    m._end = new PBPolyIter(f._pbpoly.orderedEnd())
    return m


class BooleanPolynomialIdeal(MPolynomialIdeal):
    def __init__(self, ring, gens=[], coerce=True):
        """
        Construct an ideal in the boolean polynomial ring.

        INPUT:

        -  ``ring`` - the ring this ideal is defined in

        -  ``gens`` - a list of generators

        - ``coerce`` - coerce all elements to the ring ``ring`` (default: ``True``)

        EXAMPLES::

            sage: P.<x0, x1, x2, x3> = BooleanPolynomialRing(4)
            sage: I = P.ideal(x0*x1*x2*x3 + x0*x1*x3 + x0*x1 + x0*x2 + x0)
            sage: I
            Ideal (x0*x1*x2*x3 + x0*x1*x3 + x0*x1 + x0*x2 + x0) of Boolean PolynomialRing in x0, x1, x2, x3
            sage: loads(dumps(I)) == I
            True

        """
        MPolynomialIdeal.__init__(self, ring, gens, coerce)

    def dimension(self):
        """
        Return the dimension of ``self``, which is always zero.

        TESTS:

        Check that :trac:`13155` is solved::

            sage: R = BooleanPolynomialRing(11, 'x')
            sage: R2 = PolynomialRing(GF(2), 11, 'x')
            sage: I = ideal([ R(f) for f in sage.rings.ideal.Cyclic(R2, 11).gens() ])
            sage: I.dimension()
            0
        """
        return 0

    def groebner_basis(self, algorithm='polybori', **kwds):
        """
        Return a Groebner basis of this ideal.

        INPUT:

        - ``algorithm`` - either ``"polybori"`` (built-in default)
          or ``"magma"`` (requires Magma).

        - ``red_tail`` - tail reductions in intermediate polynomials,
          this options affects mainly heuristics. The reducedness of
          the output polynomials can only be guaranteed by the option
          redsb (default: ``True``)

        - ``minsb`` - return a minimal Groebner basis (default:
          ``True``)

        - ``redsb`` - return a minimal Groebner basis and all tails
          are reduced (default: ``True``)

        - ``deg_bound`` - only compute Groebner basis up to a given
          degree bound (default: ``False``)

        - ``faugere`` - turn off or on the linear algebra (default:
          ``False``)

        - ``linear_algebra_in_last_block`` - this affects the last
          block of block orderings and degree orderings. If it is set
          to ``True`` linear algebra takes affect in this
          block. (default: ``True``)

        - ``gauss_on_linear`` - perform Gaussian elimination on linear
           polynomials (default: ``True``)

        - ``selection_size`` - maximum number of polynomials for
          parallel reductions (default: ``1000``)

        - ``heuristic`` - Turn off heuristic by setting
          ``heuristic=False`` (default: ``True``)

        - ``lazy`` - (default: ``True``)

        - ``invert`` - setting ``invert=True`` input and output get a
          transformation ``x+1`` for each variable ``x``, which shouldn't
          effect the calculated GB, but the algorithm.

        - ``other_ordering_first`` - possible values are ``False`` or
          an ordering code. In practice, many Boolean examples have
          very few solutions and a very easy Groebner basis. So, a
          complex walk algorithm (which cannot be implemented using
          the data structures) seems unnecessary, as such Groebner
          bases can be converted quite fast by the normal Buchberger
          algorithm from one ordering into another
          ordering. (default: ``False``)

        - ``prot`` - show protocol (default: ``False``)

        - ``full_prot`` - show full protocol (default: ``False``)

        EXAMPLES::

            sage: P.<x0, x1, x2, x3> = BooleanPolynomialRing(4)
            sage: I = P.ideal(x0*x1*x2*x3 + x0*x1*x3 + x0*x1 + x0*x2 + x0)
            sage: I.groebner_basis()
            [x0*x1 + x0*x2 + x0, x0*x2*x3 + x0*x3]

        Another somewhat bigger example::

            sage: sr = mq.SR(2,1,1,4,gf2=True, polybori=True)
            sage: F,s = sr.polynomial_system()
            sage: I = F.ideal()
            sage: I.groebner_basis()
            Polynomial Sequence with 36 Polynomials in 36 Variables

        We compute the same example with Magma::

            sage: sr = mq.SR(2,1,1,4,gf2=True, polybori=True)
            sage: F,s = sr.polynomial_system()
            sage: I = F.ideal()
            sage: I.groebner_basis(algorithm='magma', prot='sage') # optional - magma
            Leading term degree:  1. Critical pairs: 148.
            Leading term degree:  2. Critical pairs: 144.
            Leading term degree:  3. Critical pairs: 462.
            Leading term degree:  1. Critical pairs: 167.
            Leading term degree:  2. Critical pairs: 147.
            Leading term degree:  3. Critical pairs: 101 (all pairs of current degree eliminated by criteria).
            <BLANKLINE>
            Highest degree reached during computation:  3.
            Polynomial Sequence with 35 Polynomials in 36 Variables

        TESTS:

        This example shows, that a bug in our variable indices was
        indeed fixed::

            sage: R.<a111,a112,a121,a122,b111,b112,b211,b212,c111,c112> = BooleanPolynomialRing(order='lex')
            sage: I = (a111 * b111 * c111 + a112 * b112 * c112 - 1, a111 * b211 * c111 + a112 * b212 * c112 - 0,
            ....:      a121 * b111 * c111 + a122 * b112 * c112, a121 * b211 * c111 + a122 * b212 * c112 - 1)*R
            sage: I.groebner_basis()
            [a111 + b212, a112 + b211, a121 + b112, a122 + b111, b111*b112 + b111 + b112 + 1,
             b111*b211 + b111 + b211 + 1, b111*b212 + b112*b211 + 1, b112*b212 + b112 + b212 + 1,
             b211*b212 + b211 + b212 + 1, c111 + 1, c112 + 1]


        The following example shows whether boolean constants are handled correctly::

            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: I = Ideal([x*z + y*z + z, x*y + x*z + x + y*z + y + z])
            sage: I.groebner_basis()
            [x, y, z]

        Check that this no longer crash (:trac:`12792`)::

            sage: names = [ "s{0}s{1}".format(i,j) for i in range(4) for j in range(8)]
            sage: R = BooleanPolynomialRing(32, names)
            sage: R.inject_variables()
            Defining s0s0, ...
            sage: problem = [s1s0*s1s1, s0s0*s0s1 + s0s0 + s0s1 + s2s0 + s3s0*s3s1 + s3s0 + s3s1,
            ....:            s1s1 + s2s0 + s3s0 + s3s1 + 1, s0s0*s0s1 + s1s1 + s3s0*s3s1 + s3s0,
            ....:            s0s1 + s1s0 + s1s1 + s3s0, s0s0*s0s1 + s0s0 + s0s1 + s1s1 + s2s0 + s3s1,
            ....:            s0s1 + s1s0, s0s0*s0s1 + s0s0 + s0s1 + s1s0 + s2s0 + s3s1,
            ....:            s0s0 + s2s0 + s3s0*s3s1 + s3s0 + 1, s0s0 + s1s1]
            sage: ideal(problem).groebner_basis()
            [1]

        """
        try:
            return Sequence(sorted(self.__gb, reverse=True), self.ring(), check=False, immutable=True)
        except AttributeError:
            pass

        if algorithm == 'magma':
            from sage.rings.polynomial.multi_polynomial_ideal import MPolynomialIdeal_magma_repr
            gb = MPolynomialIdeal_magma_repr._groebner_basis_magma(self, **kwds)
        else:
            if "redsb" not in kwds:
                kwds["redsb"]=True
            sig_on()
            gb = self._groebner_basis(**kwds)
            sig_off()

        if kwds.get("deg_bound", False) is False:
            g = GroebnerStrategy(gb[0].ring())
            for p in gb:
                g.add_as_you_wish(p)
            g.reduction_strategy.opt_red_tail=True
            self.__gb = g

        return Sequence(sorted(gb,reverse=True), self.ring(), check=False, immutable=True)

    def _groebner_basis(self, **kwds):
        r"""
        Calls PolyBoRi's groebner_basis function. It takes care of the import
        and suitable wrapping (if necessary)

        EXAMPLES::

            sage: B.<x,y,z> = BooleanPolynomialRing(order='deglex')
            sage: id = B.ideal((x + y)*(y + z), x*y*z)
            sage: id._groebner_basis()
            [x*z, x*y + y*z + y]

            sage: B.<x,y,z> = BooleanPolynomialRing(order='deglex')
            sage: id = B.ideal((x + y)*(y + z), x*y*z)
            sage: id._groebner_basis()
            [x*z, x*y + y*z + y]
        """

        from brial.gbcore import groebner_basis

        if self.ring().term_order()[0].name() == "degrevlex":
            # PolyBoRi's groebner_basis assumes increasing indices
            # so undone degneglex (dp_asc) wrapping for now
            tmp = BooleanPolynomialRing_from_PBRing((<BooleanPolynomialRing>self.ring())._pbring)
            gb = groebner_basis([new_BP_from_PBPoly(tmp, (<BooleanPolynomial>elt)._pbpoly) \
              for elt in self.gens()], **kwds)
            return [new_BP_from_PBPoly(self.ring(), (<BooleanPolynomial>elt)._pbpoly) for elt in gb]

        return groebner_basis(self.gens(), **kwds)

    def variety(self, **kwds):
        r"""
        Return the variety associated to this boolean ideal.

        EXAMPLES:

        A simple example::

            sage: from sage.doctest.fixtures import reproducible_repr
            sage: R.<x,y,z> = BooleanPolynomialRing()
            sage: I = ideal( [ x*y*z + x*z + y + 1, x+y+z+1 ] )
            sage: print(reproducible_repr(I.variety()))
            [{x: 0, y: 1, z: 0}, {x: 1, y: 1, z: 1}]

        TESTS:

        BooleanIdeal and regular (quotient) Ideal should coincide::

            sage: R = BooleanPolynomialRing(6, ['x%d'%(i+1) for i in range(6)], order='lex')
            sage: R.inject_variables()
            Defining...
            sage: polys = [
            ....:     x1*x2 + x1*x4 + x1*x5 + x1*x6 + x1 + x2 + x3*x4 + x3*x5 + x3 + x4*x5 + x4*x6 + x4 + x5 + x6,
            ....:     x1*x2 + x1*x3 + x1*x4 + x1*x6 + x2*x3 + x2*x6 + x2 + x3*x4 + x5*x6,
            ....:     x1*x3 + x1*x4 + x1*x6 + x1 + x2*x5 + x2*x6 + x3*x4 + x3 + x4*x6 + x4 + x5*x6 + x5 + x6,
            ....:     x1*x2 + x1*x3 + x1*x4 + x1*x5 + x2 + x3*x5 + x3*x6 + x3 + x5 + x6,
            ....:     x1*x2 + x1*x4 + x1*x5 + x1*x6 + x2*x3 + x2*x4 + x2*x5 + x3*x5 + x5*x6 + x5 + x6,
            ....:     x1*x2 + x1*x6 + x2*x4 + x2*x5 + x2*x6 + x3*x6 + x4*x6 + x5*x6 + x5]
            sage: I = R.ideal( polys )
            sage: print(reproducible_repr(I.variety()))
             [{x1: 0, x2: 0, x3: 0, x4: 0, x5: 0, x6: 0}, {x1: 1, x2: 1, x3: 1, x4: 0, x5: 0, x6: 1}]

            sage: R = PolynomialRing(GF(2), 6, ['x%d'%(i+1) for i in range(6)], order='lex')
            sage: I = R.ideal( polys )
            sage: v = (I + sage.rings.ideal.FieldIdeal(R)).variety()
            sage: print(reproducible_repr(v))
            [{x1: 0, x2: 0, x3: 0, x4: 0, x5: 0, x6: 0}, {x1: 1, x2: 1, x3: 1, x4: 0, x5: 0, x6: 1}]


        Check that :trac:`13976` is fixed::

            sage: R.<x,y,z> = BooleanPolynomialRing()
            sage: I = ideal( [ x*y*z + x*z + y + 1, x+y+z+1 ] )
            sage: sols = I.variety()
            sage: sols[0][y]
            1

        Make sure the result is a key converting dict, as discussed in
        :trac:`9788` and consistent with
        :meth:`sage.rings.polynomial.multi_polynomial_ideal.MPolynomialIdeal_singular_repr.variety`::

            sage: sols[0]["y"]
            1

        """
        from sage.misc.converting_dict import KeyConvertingDict
        R_bool = self.ring()
        R = R_bool.cover_ring()
        I = R.ideal([R(f) for f in self.groebner_basis()])
        J = FieldIdeal(R)
        solutions = (I + J).variety(**kwds)
        return [KeyConvertingDict(R_bool, s) for s in solutions]

    def reduce(self, f):
        """
        Reduce an element modulo the reduced Groebner basis for this ideal.
        This returns 0 if and only if the element is in this ideal. In any
        case, this reduction is unique up to monomial orders.

        EXAMPLES::

            sage: P = PolynomialRing(GF(2),10, 'x')
            sage: B = BooleanPolynomialRing(10,'x')
            sage: I = sage.rings.ideal.Cyclic(P)
            sage: I = B.ideal([B(f) for f in I.gens()])
            sage: gb = I.groebner_basis()
            sage: I.reduce(gb[0])
            0
            sage: I.reduce(gb[0] + 1)
            1
            sage: I.reduce(gb[0]*gb[1])
            0
            sage: I.reduce(gb[0]*B.gen(1))
            0
        """
        from brial import red_tail
        try:
            g = self.__gb
        except AttributeError:
            self.groebner_basis()
            g = self.__gb
        g.reduction_strategy.opt_red_tail=True
        p = g.nf(f)
        return p

    def interreduced_basis(self):
        """
        If this ideal is spanned by ``(f_1, ..., f_n)`` this method
        returns ``(g_1, ..., g_s)`` such that:

        -  ``<f_1,...,f_n> = <g_1,...,g_s>``
        -  ``LT(g_i) != LT(g_j)`` for all ``i != j```
        - ``LT(g_i)`` does not divide ``m`` for all monomials ``m`` of
          ``{g_1,...,g_{i-1},g_{i+1},...,g_s}``

        EXAMPLES::

            sage: sr = mq.SR(1, 1, 1, 4, gf2=True, polybori=True)
            sage: F,s = sr.polynomial_system()
            sage: I = F.ideal()
            sage: I.interreduced_basis()
            [k100 + 1, k101 + k001 + 1, k102, k103 + 1, x100 + k001 + 1, x101 + k001, x102, x103 + k001, w100 + 1, w101 + k001 + 1, w102 + 1, w103 + 1, s000 + k001, s001 + k001 + 1, s002, s003 + k001 + 1, k000 + 1, k002 + 1, k003 + 1]
        """
        return self.basis.reduced()

    def __eq__(self, other):
        """
        EXAMPLES::
            sage: sr = mq.SR(1, 1, 1, 4, gf2=True, polybori=True)
            sage: F,s = sr.polynomial_system()
            sage: I = F.ideal()
            sage: J = Ideal(I.interreduced_basis())
            sage: I == J
            True
            sage: J = Ideal(I.gens()[1:] + [I.gens()[0] + 1])
            sage: I == J
            False
        """
        if not isinstance(other, BooleanPolynomialIdeal):
            return False
        elif self.ring() != other.ring():
            return False
        else:
            return self.groebner_basis() == other.groebner_basis()

    def __ne__(self, other):
        """
        EXAMPLES::
            sage: sr = mq.SR(1, 1, 1, 4, gf2=True, polybori=True)
            sage: F,s = sr.polynomial_system()
            sage: I = F.ideal()
            sage: J = Ideal(I.interreduced_basis())
            sage: I != J
            False
            sage: J = Ideal(I.gens()[1:] + [I.gens()[0] + 1])
            sage: I != J
            True
        """
        return not self.__eq__(other)

##
#
# Various internal constructors for boolean polynomials from various
# other formats.
#
##

cdef inline BooleanPolynomial new_BP(BooleanPolynomialRing parent):
    cdef BooleanPolynomial p
    p = <BooleanPolynomial>BooleanPolynomial.__new__(BooleanPolynomial)
    p._parent = parent
    return p


cdef inline BooleanPolynomial new_BP_from_PBVar(BooleanPolynomialRing parent, PBVar juice):
    cdef BooleanPolynomial p = new_BP(parent)
    p._pbpoly = PBBoolePolynomial(juice)
    return p


cdef inline BooleanPolynomial new_BP_from_PBPoly(BooleanPolynomialRing parent, PBPoly juice):
    cdef BooleanPolynomial p = new_BP(parent)
    p._pbpoly = juice
    return p

cdef inline BooleanPolynomial new_BP_from_PBMonom(BooleanPolynomialRing parent, PBMonom juice):
    cdef BooleanPolynomial p = new_BP(parent)
    p._pbpoly = PBBoolePolynomial(juice)
    return p

cdef inline BooleanPolynomial new_BP_from_PBSet(BooleanPolynomialRing parent, PBSet juice):
    cdef BooleanPolynomial p = new_BP(parent)
    p._pbpoly = PBBoolePolynomial(juice)
    return p

cdef inline BooleanPolynomial new_BP_from_int(BooleanPolynomialRing parent, int juice):
    cdef BooleanPolynomial p = new_BP(parent)
    p._pbpoly = PBBoolePolynomial(juice, parent._pbring)
    return p


cdef class BooleSet:
    """
    Return a new set of boolean monomials. This data type is also
    implemented on the top of ZDDs and allows to see polynomials from
    a different angle. Also, it makes high-level set operations
    possible, which are in most cases faster than operations handling
    individual terms, because the complexity of the algorithms depends
    only on the structure of the diagrams.

    Objects of type :class:`BooleanPolynomial` can easily be converted
    to the type :class:`BooleSet` by using the member function
    :meth:`BooleanPolynomial.set()`.

    INPUT:

    - ``param`` - either a :class:`CCuddNavigator`, a :class:`BooleSet` or ``None``.
    - ``ring`` - a boolean polynomial ring.

    EXAMPLES::

        sage: from brial import BooleSet
        sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
        sage: BS = BooleSet(a.set())
        sage: BS
        {{a}}

        sage: BS = BooleSet((a*b + c + 1).set())
        sage: BS
        {{a,b}, {c}, {}}

        sage: from brial import *
        sage: BooleSet([Monomial(B)])
        {{}}

    .. NOTE::

      :class:`BooleSet` prints as ``{}`` but are not Python dictionaries.
    """
    def __init__(self, param=None, ring=None):
        cdef BooleanPolynomial p
        if isinstance(param, CCuddNavigator):
            if ring is None:
                raise TypeError("BooleSet constructor requires parent ring argument")
            self._ring = ring
            self._pbset = PBBooleSet((<CCuddNavigator>param)._pbnav,
                                     (<BooleanPolynomialRing>ring)._pbring)
        elif isinstance(param, BooleSet):
            self._pbset = (<BooleSet>param)._pbset
            self._ring = (<BooleSet>param)._ring
        elif isinstance(param, BooleanPolynomial):
            self._pbset = PBBooleSet((<BooleanPolynomial>param)._pbpoly)
            self._ring = (<BooleanPolynomial>param)._parent
        elif isinstance(param, BooleanPolynomialRing):
            self._pbset = PBBooleSet((<BooleanPolynomialRing>param)._pbring)
            self._ring = param
        else:
            terms = list(param)
            detected_ring = None

            if terms:
                detected_ring = terms[0].ring()
            elif isinstance(ring, BooleanPolynomialRing):
                detected_ring = ring

            if detected_ring is None:
                raise TypeError(
                    "BooleSet: could not extract ring from %s, %s" %
                    (type(param), str(type(ring))))

            p = sum(terms)
            self._pbset = PBBooleSet((<BooleanPolynomial>p)._pbpoly)
            self._ring = detected_ring

    def __repr__(self):
        """
        EXAMPLES::

            sage: from brial import BooleSet
            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: BS = BooleSet(B)
            sage: repr(BS) # indirect doctest
            '{}'
        """
        return ccrepr(self._pbset)

    def set(self):
        """
        Return ``self``.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: BS = (a*b + c).set()
            sage: BS.set() is BS
            True
        """
        return self

    def empty(self):
        """
        Return ``True`` if this set is empty.

        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
            sage: BS = (a*b + c).set()
            sage: BS.empty()
            False

            sage: BS = B(0).set()
            sage: BS.empty()
            True
        """
        return self._pbset.isZero()

    def navigation(self):
        """
        Navigators provide an interface to diagram nodes, accessing
        their index as well as the corresponding then- and
        else-branches.

        You should be very careful and always keep a reference to the
        original object, when dealing with navigators, as navigators
        contain only a raw pointer as data. For the same reason, it is
        necessary to supply the ring as argument, when constructing a
        set out of a navigator.

        EXAMPLES::

            sage: from brial import BooleSet
            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3*x4+x2*x4+x3+x4+1
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3,x4}, {x2,x4}, {x3}, {x4}, {}}

            sage: nav = s.navigation()
            sage: BooleSet(nav,s.ring())
            {{x1,x2}, {x2,x3,x4}, {x2,x4}, {x3}, {x4}, {}}

            sage: nav.value()
            1

            sage: nav_else = nav.else_branch()

            sage: BooleSet(nav_else,s.ring())
            {{x2,x3,x4}, {x2,x4}, {x3}, {x4}, {}}

            sage: nav_else.value()
            2
        """
        return new_CN_from_PBNavigator(self._pbset.navigation(),
                                       (<BooleanPolynomialRing>self._ring).pbind)

    def ring(self):
        """
        Return the parent ring.

        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3*x4+x2*x4+x3+x4+1
            sage: f.set().ring() is B
            True
        """
        return self._ring

    def cartesian_product(self, rhs):
        r"""
        Return the Cartesian product of this set and the set ``rhs``.

        The Cartesian product of two sets X and Y is the set of all
        possible ordered pairs whose first component is a member of X and
        whose second component is a member of Y.


        .. MATH::

            X\times Y = \{(x,y) | x\in X\;\mathrm{and}\;y\in Y\}.



        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: g = x4 + 1
            sage: t = g.set(); t
            {{x4}, {}}
            sage: s.cartesian_product(t)
            {{x1,x2,x4}, {x1,x2}, {x2,x3,x4}, {x2,x3}}
        """
        return new_BS_from_PBSet(
                self._pbset.cartesianProduct((<BooleSet?>rhs)._pbset), self._ring)

    def diff(self, rhs):
        r"""
        Return the set theoretic difference of this set and the set
        ``rhs``.

        The difference of two sets `X` and `Y` is defined as:


        .. MATH::

            X \ Y = \{x | x\in X\;\mathrm{and}\;x\not\in Y\}.


        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: g = x2*x3 + 1
            sage: t = g.set(); t
            {{x2,x3}, {}}
            sage: s.diff(t)
            {{x1,x2}}
        """
        cdef PBSet s
        if isinstance(rhs, BooleSet):
            s = (<BooleSet>rhs)._pbset
        elif isinstance(rhs, BooleanPolynomial):
            s = (<BooleanPolynomial>rhs)._pbpoly.set()
        else:
            raise TypeError("Argument 'rhs' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(rhs))
        return new_BS_from_PBSet(self._pbset.diff(s), self._ring)

    def union(self, rhs):
        r"""
        Return the set theoretic union of this set and the set
        ``rhs``.

        The union of two sets `X` and `Y` is defined as:

        .. MATH::

            X \cup Y = \{x | x\in X\;\mathrm{or}\;x\in Y\}.


        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: g = x2*x3 + 1
            sage: t = g.set(); t
            {{x2,x3}, {}}
            sage: s.union(t)
            {{x1,x2}, {x2,x3}, {}}
        """
        cdef PBSet s
        if isinstance(rhs, BooleSet):
            s = (<BooleSet>rhs)._pbset
        elif isinstance(rhs, BooleanPolynomial):
            s = (<BooleanPolynomial>rhs)._pbpoly.set()
        else:
            raise TypeError("Argument 'rhs' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(rhs))
        return new_BS_from_PBSet(self._pbset.unite(s), self._ring)

    def change(self, ind):
        """
        Swaps the presence of ``x_i`` in each entry of the set.

        EXAMPLES::

            sage: P.<a,b,c> = BooleanPolynomialRing()
            sage: f = a+b
            sage: s = f.set(); s
            {{a}, {b}}
            sage: s.change(0)
            {{a,b}, {}}
            sage: s.change(1)
            {{a,b}, {}}
            sage: s.change(2)
            {{a,c}, {b,c}}
        """
        return new_BS_from_PBSet(self._pbset.change(self._ring.pbind[ind]), self._ring)

    def vars(self):
        """
        Return the variables in this set as a monomial.

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing(order='lex')
            sage: f = a + b*e + d*f + e + 1
            sage: s = f.set()
            sage: s
            {{a}, {b,e}, {d,f}, {e}, {}}
            sage: s.vars()
            a*b*d*e*f
        """
        return new_BM_from_PBMonom(self._ring._monom_monoid, self._ring,
                                            self._pbset.usedVariables())

    def n_nodes(self):
        """
        Return the number of nodes in the ZDD.

        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: s.n_nodes()
            4
        """
        return self._pbset.nNodes()

    def __iter__(self):
        """
        Create an iterator over elements of self.

        EXAMPLES::

            sage: P.<x, y> = BooleanPolynomialRing(2)
            sage: f = x*y+x+y+1; s = f.set()
            sage: list(s)
            [x*y, x, y, 1]
        """
        return new_BSI_from_PBSetIter(self)

    def __len__(self):
        """
        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: len(s)
            2
        """
        return self._pbset.size()

    def __hash__(self):
        """
        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: {s:1}
            {{{x1,x2}, {x2,x3}}: 1}
        """
        return <Py_ssize_t>(self._pbset.stableHash())

    def __mod__(self, BooleSet vs):
        """
        Return a set of all monomials which are not divisible by
        monomials in ``vs``.

        INPUT:

        - ``vs`` - a boolean set

        EXAMPLES::

            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: f = a*b + b + 1
            sage: s = f.set(); s
            {{a,b}, {b}, {}}
            sage: s % a.set()
            {{b}, {}}
            sage: s % b.set()
            {{}}
        """
        return mod_mon_set(self, vs)

    def __contains__(self, BooleanMonomial m):
        """
        Return ``True`` if ``m`` is in this set.

        INPUT:

        - ``m`` - a monomial

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: f = a*b
            sage: s  = f.set()
            sage: a.lm() in s
            False

        TESTS::

            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: f = a*b
            sage: s  = f.set()
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: a.lm() in s
            Traceback (most recent call last):
            ...
            AssertionError
        """
        assert(m._ring is self._ring)
        return self._pbset.owns(m._pbmonom)

    def stable_hash(self):
        """
        A hash value which is stable across processes.

        EXAMPLES::

            sage: B.<x,y> = BooleanPolynomialRing()
            sage: x.set() is x.set()
            False
            sage: x.set().stable_hash() == x.set().stable_hash()
            True

        .. NOTE::

           This function is part of the upstream PolyBoRi
           interface. In Sage all hashes are stable.
        """
        return <Py_ssize_t>(self._pbset.stableHash())

    def divide(self, BooleanMonomial rhs):
        """
        Divide each element of this set by the monomial ``rhs`` and
        return a new set containing the result.

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing(order='lex')
            sage: f = b*e + b*c*d + b
            sage: s = f.set(); s
            {{b,c,d}, {b,e}, {b}}
            sage: s.divide(b.lm())
            {{c,d}, {e}, {}}

            sage: f = b*e + b*c*d + b + c
            sage: s = f.set()
            sage: s.divide(b.lm())
            {{c,d}, {e}, {}}
        """
        return new_BS_from_PBSet(self._pbset.divide(rhs._pbmonom), self._ring)

    def subset0(self, int i):
        """
        Return a set of those elements in this set which do not
        contain the variable indexed by ``i``.

        INPUT:

        - ``i`` - an index

        EXAMPLES::

            sage: BooleanPolynomialRing(5,'x')
            Boolean PolynomialRing in x0, x1, x2, x3, x4
            sage: B = BooleanPolynomialRing(5,'x')
            sage: B.inject_variables()
            Defining x0, x1, x2, x3, x4
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: s.subset0(1)
            {{x2,x3}}
        """
        return new_BS_from_PBSet(self._pbset.subset0(self._ring.pbind[i]), self._ring)

    def subset1(self, int i):
        """
        Return a set of those elements in this set which do contain
        the variable indexed by ``i`` and evaluate the variable
        indexed by ``i`` to 1.

        INPUT:

        - ``i`` - an index

        EXAMPLES::

            sage: BooleanPolynomialRing(5,'x')
            Boolean PolynomialRing in x0, x1, x2, x3, x4
            sage: B = BooleanPolynomialRing(5,'x')
            sage: B.inject_variables()
            Defining x0, x1, x2, x3, x4
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: s.subset1(1)
            {{x2}}
        """
        return new_BS_from_PBSet(self._pbset.subset1(self._ring.pbind[i]), self._ring)

    def include_divisors(self):
        """
        Extend this set to include all divisors of the elements
        already in this set and return the result as a new set.

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: f = a*d*e + a*f + b*d*e + c*d*e + 1
            sage: s = f.set(); s
            {{a,d,e}, {a,f}, {b,d,e}, {c,d,e}, {}}

            sage: s.include_divisors()
            {{a,d,e}, {a,d}, {a,e}, {a,f}, {a}, {b,d,e}, {b,d}, {b,e},
             {b}, {c,d,e}, {c,d}, {c,e}, {c}, {d,e}, {d}, {e}, {f}, {}}
        """
        return new_BS_from_PBSet(pb_include_divisors(self._pbset), self._ring)

    def minimal_elements(self):
        """
        Return a new set containing a divisor of all elements of this set.

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: f = a*d*e + a*f + a*b*d*e + a*c*d*e + a
            sage: s = f.set(); s
            {{a,b,d,e}, {a,c,d,e}, {a,d,e}, {a,f}, {a}}
            sage: s.minimal_elements()
            {{a}}
        """
        return new_BS_from_PBSet(pb_minimal_elements(self._pbset), self._ring)

    def intersect(self, BooleSet other):
        r"""
        Return the set theoretic intersection of this set and the set
        ``rhs``.

        The union of two sets `X` and `Y` is defined as:


        .. MATH::

            X \cap Y = \{x | x\in X\;\mathrm{and}\;x\in Y\}.


        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set(); s
            {{x1,x2}, {x2,x3}}
            sage: g = x2*x3 + 1
            sage: t = g.set(); t
            {{x2,x3}, {}}
            sage: s.intersect(t)
            {{x2,x3}}
        """
        return new_BS_from_PBSet(self._pbset.intersect(other._pbset), self._ring)

    def divisors_of(self, BooleanMonomial m):
        """
        Return those members which are divisors of ``m``.

        INPUT:

        - ``m`` - a boolean monomial

        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set()
            sage: s.divisors_of((x1*x2*x4).lead())
            {{x1,x2}}
        """
        return new_BS_from_PBSet(self._pbset.divisorsOf(m._pbmonom), self._ring)

    def multiples_of(self, BooleanMonomial m):
        """
        Return those members which are multiples of ``m``.

        INPUT:

        - ``m`` - a boolean monomial

        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set()
            sage: s.multiples_of(x1.lm())
            {{x1,x2}}
        """
        return new_BS_from_PBSet(self._pbset.multiplesOf(m._pbmonom), self._ring)

    def size_double(self):
        """
        Return the size of this set as a floating point number.

        EXAMPLES::

            sage: B = BooleanPolynomialRing(5,'x')
            sage: x0,x1,x2,x3,x4 = B.gens()
            sage: f = x1*x2+x2*x3
            sage: s = f.set()
            sage: s.size_double()
            2.0
        """
        return self._pbset.sizeDouble()


cdef inline BooleSet new_BS_from_PBSet(PBSet juice, BooleanPolynomialRing ring):
    """
    Construct a new BooleSet
    """
    cdef BooleSet s
    s = <BooleSet>BooleSet.__new__(BooleSet)
    s._pbset = juice
    s._ring = ring

    return s


cdef class BooleSetIterator:
    """
    Helper class to iterate over boolean sets.
    """
    def __dealloc__(self):
        del self._iter
        del self._end

    def __iter__(self):
        """
        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: f = B.random_element()
            sage: it = iter(f.set()) # indirect doctest
        """
        return self

    def __next__(self):
        """
        EXAMPLES::

            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: f = B.random_element()
            sage: f
            a*b + a*c + a + b*d + 1
            sage: it = iter(f.set())
            sage: next(it)
            a*b
        """
        cdef PBMonom value
        if deref(self._iter) == deref(self._end):
            raise StopIteration
        value = self._iter.dereference()
        self._iter.increment()
        return new_BM_from_PBMonom(self._parent, self._ring, value)


cdef inline BooleSetIterator new_BSI_from_PBSetIter(BooleSet s):
    """
    Construct a new BooleSetIterator
    """
    cdef BooleSetIterator m
    m = <BooleSetIterator>BooleSetIterator.__new__(BooleSetIterator)
    m._ring = s._ring
    m._parent = m._ring._monom_monoid
    m.obj = s
    m._iter = new PBSetIter(s._pbset.begin())
    m._end = new PBSetIter(s._pbset.end())
    return m


cdef class CCuddNavigator:
    def __call__(self):
        return self

    def value(self):
        if self._pbnav.isConstant():
            return self._pbnav.value()
        return self._pbind[self._pbnav.value()]

    def else_branch(self):
        return new_CN_from_PBNavigator(self._pbnav.elseBranch(), self._pbind)

    def then_branch(self):
        return new_CN_from_PBNavigator(self._pbnav.thenBranch(), self._pbind)

    def constant(self):
        return self._pbnav.isConstant()

    def terminal_one(self):
        return self._pbnav.isTerminated()

    def __richcmp__(CCuddNavigator self, CCuddNavigator other, int op):
        """
        ::

            sage: R.<x,y>=BooleanPolynomialRing(2)
            sage: p = R(0)
            sage: p.navigation() == p.navigation()
            True
            sage: p.navigation() != p.navigation()
            False
            sage: p.navigation() == x.navigation()
            False
        """
        cdef bint equal = (self._pbnav == other._pbnav)

        if op == Py_EQ:
            return equal
        elif op == Py_NE:
            return not equal
        else:
            return NotImplemented

    def __hash__(self):
        return self._pbnav.hash()


cdef class BooleanPolynomialVector:
    """
    A vector of boolean polynomials.

    EXAMPLES::

        sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
        sage: from brial import BooleanPolynomialVector
        sage: l = [B.random_element() for _ in range(3)]
        sage: v = BooleanPolynomialVector(l)
        sage: len(v)
        3
        sage: v[0]
        a*b + a + b*e + c*d + e*f
        sage: list(v)
        [a*b + a + b*e + c*d + e*f, a*d + c*d + d*f + e + f, a*c + a*e + b*c + c*f + f]
    """
    def __init__(self, I=None):
        """
        Create a new :class:`BooleanPolynomialVector`.

        INPUT:

        - ``I`` - a list of boolean polynomials.

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import BooleanPolynomialVector
            sage: l = [B.random_element() for _ in range(3)]
            sage: v = BooleanPolynomialVector(l)
            sage: len(v)
            3
            sage: v[0]
            a*b + a + b*e + c*d + e*f
            sage: list(v)
            [a*b + a + b*e + c*d + e*f, a*d + c*d + d*f + e + f, a*c + a*e + b*c + c*f + f]
        """
        # This is used by PolyBoRi python code
        self._parent = None
        if I is not None:
            if I:
                self._parent = I[0].ring()
            for f in I:
                self.append(f)

    def __iter__(self):
        """
        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import BooleanPolynomialVector
            sage: l = [B.random_element() for _ in range(3)]
            sage: v = BooleanPolynomialVector(l)
            sage: list(iter(v))
            [a*b + a + b*e + c*d + e*f, a*d + c*d + d*f + e + f, a*c + a*e + b*c + c*f + f]
        """
        return new_BPVI_from_PBPolyVectorIter(self)

    def __len__(self):
        """
        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import BooleanPolynomialVector
            sage: l = [B.random_element() for _ in range(3)]
            sage: v = BooleanPolynomialVector()
            sage: len(v)
            0
            sage: v = BooleanPolynomialVector(l)
            sage: len(v)
            3
        """
        return self._vec.size()

    def __getitem__(self, Py_ssize_t i):
        """
        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import BooleanPolynomialVector
            sage: l = [B.random_element() for _ in range(3)]
            sage: v = BooleanPolynomialVector(l)
            sage: len(v)
            3
            sage: v[0]
            a*b + a + b*e + c*d + e*f
            sage: v[-1]
            a*c + a*e + b*c + c*f + f
            sage: v[3]
            Traceback (most recent call last):
            ...
            IndexError: index out of range
            sage: v['a']
            Traceback (most recent call last):
            ...
            TypeError: 'str' object cannot be interpreted as an i...
        """
        if i < 0:
            i += self._vec.size()
        if i < 0 or <size_t>i >= self._vec.size():
            raise IndexError("index out of range")
        cdef PBPoly value = self._vec[i]
        return new_BP_from_PBPoly(self._parent, value)

    def __setitem__(self, Py_ssize_t i, p):
        """
        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import BooleanPolynomialVector
            sage: l = [B.random_element() for _ in range(3)]
            sage: v = BooleanPolynomialVector(l)
            sage: len(v)
            3
            sage: v[0] = a; v[0]
            a
            sage: v[-1] = b; v[-1]
            b
            sage: v[3] = c
            Traceback (most recent call last):
            ...
            IndexError
        """
        if not self._parent:
            self._parent = p.ring()
        if i < 0:
            i += self._vec.size()
        if i < 0 or <size_t>i >= self._vec.size():
            raise IndexError
        if not isinstance(p, BooleanPolynomialVector):
            p = self._parent(p)

        self._vec[i] = (<BooleanPolynomial>p)._pbpoly

    def append(self, el):
        """
        Append the element ``el`` to this vector.

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import BooleanPolynomialVector
            sage: v = BooleanPolynomialVector()
            sage: for i in range(5):
            ....:   v.append(B.random_element())

            sage: list(v)
            [a*b + a + b*e + c*d + e*f, a*d + c*d + d*f + e + f, a*c + a*e + b*c + c*f + f, a*c + a*d + a*e + a*f + b*e, b*c + b*d + c*d + c + 1]
        """
        if not self._parent:
            self._parent = el.ring()
        cdef PBPoly p
        if isinstance(el, BooleanPolynomial):
            p = (<BooleanPolynomial>el)._pbpoly
        elif isinstance(el, BooleanMonomial):
            p = PBBoolePolynomial((<BooleanMonomial>el)._pbmonom)
        else:
            raise TypeError("Argument 'el' has incorrect type (expected BooleanPolynomial or BooleanMonomial, got %s)" % type(el))
        self._vec.push_back(<PBBoolePolynomial>p)

cdef inline BooleanPolynomialVector new_BPV_from_PBPolyVector(
        BooleanPolynomialRing parent, PBPolyVector juice):
    cdef BooleanPolynomialVector m
    m = <BooleanPolynomialVector>BooleanPolynomialVector.__new__(BooleanPolynomialVector)
    m._vec = juice
    m._parent = parent
    return m


cdef class BooleanPolynomialVectorIterator:
    def __iter__(self):
        return self

    def __next__(self):
        if self._iter == self._end:
            raise StopIteration

        cdef PBPoly value = deref(self._iter)
        self._iter += 1
        return new_BP_from_PBPoly(self._parent, value)


cdef inline BooleanPolynomialVectorIterator new_BPVI_from_PBPolyVectorIter(
        BooleanPolynomialVector vec):
    """
    Construct a new BooleanPolynomialVectorIterator
    """
    cdef BooleanPolynomialVectorIterator m
    m = <BooleanPolynomialVectorIterator>BooleanPolynomialVectorIterator.__new__(BooleanPolynomialVectorIterator)
    m._parent = vec._parent
    m.obj = vec
    m._iter = vec._vec.begin()
    m._end = vec._vec.end()
    return m


cdef class ReductionStrategy:
    """
    Functions and options for boolean polynomial reduction.
    """
    def __init__(self, ring):
        """
        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: del red
        """
        self._strat = make_shared[PBRedStrategy]((<BooleanPolynomialRing?>ring)._pbring)
        self._parent = ring

    def add_generator(self, BooleanPolynomial p):
        """
        Add the new generator ``p`` to this strategy.

        INPUT:

        - ``p`` - a boolean polynomial.

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.add_generator(x)
            sage: list([f.p for f in red])
            [x]

        TESTS:

        Check if :trac:`8966` is fixed::

            sage: red = ReductionStrategy(B)
            sage: red.add_generator(None)
            Traceback (most recent call last):
            ...
            TypeError: argument must be a BooleanPolynomial.
        """
        if p is None:
            raise TypeError("argument must be a BooleanPolynomial.")
        if p._pbpoly.isZero():
            raise ValueError("zero generators not allowed.")
        deref(self._strat).addGenerator(p._pbpoly)

    def nf(self, BooleanPolynomial p):
        """
        Compute the normal form of ``p`` w.r.t. to the generators of
        this reduction strategy object.

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.add_generator(x + y + 1)
            sage: red.add_generator(y*z + z)
            sage: red.nf(x)
            y + 1

            sage: red.nf(y*z + x)
            y + z + 1
        """
        return new_BP_from_PBPoly(self._parent, deref(self._strat).nf(p._pbpoly))

    def reduced_normal_form(self, BooleanPolynomial p):
        """
        Compute the normal form of ``p`` with respect to the
        generators of this strategy and perform tail reductions.

        INPUT:

        - ``p`` - a polynomial

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.add_generator(x + y + 1)
            sage: red.add_generator(y*z + z)
            sage: red.reduced_normal_form(x)
            y + 1

            sage: red.reduced_normal_form(y*z + x)
            y + z + 1
        """
        return new_BP_from_PBPoly(self._parent, deref(self._strat).reducedNormalForm(p._pbpoly))

    def head_normal_form(self, BooleanPolynomial p):
        """
        Compute the normal form of ``p`` with respect to the
        generators of this strategy but do not perform tail any
        reductions.

        INPUT:

        - ``p`` -- a polynomial

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.opt_red_tail = True
            sage: red.add_generator(x + y + 1)
            sage: red.add_generator(y*z + z)

            sage: red.head_normal_form(x + y*z)
            y + z + 1

            sage: red.nf(x + y*z)
            y + z + 1
        """
        return new_BP_from_PBPoly(self._parent, deref(self._strat).headNormalForm(p._pbpoly))

    def can_rewrite(self, BooleanPolynomial p):
        """
        Return ``True`` if ``p`` can be reduced by the generators of
        this strategy.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.add_generator(a*b + c + 1)
            sage: red.add_generator(b*c + d + 1)
            sage: red.can_rewrite(a*b + a)
            True
            sage: red.can_rewrite(b + c)
            False
            sage: red.can_rewrite(a*d + b*c + d + 1)
            True
        """
        return deref(self._strat).canRewrite(p._pbpoly)

    def cheap_reductions(self, BooleanPolynomial p):
        """
        Perform 'cheap' reductions on ``p``.

        INPUT:

        - ``p`` - a boolean polynomial

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c,d> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.add_generator(a*b + c + 1)
            sage: red.add_generator(b*c + d + 1)
            sage: red.add_generator(a)
            sage: red.cheap_reductions(a*b + a)
            0
            sage: red.cheap_reductions(b + c)
            b + c
            sage: red.cheap_reductions(a*d + b*c + d + 1)
            b*c + d + 1
        """
        cdef PBPoly poly = cheap_reductions(deref(self._strat), p._pbpoly)
        return new_BP_from_PBPoly(self._parent, poly)

    def __getattr__(self, name):
        """
        Get attributes of this reduction strategy object.

        SUPPORTED OPTIONS:

        - ``opt_ll`` - use linear algebra (default: ``False``)

        - ``opt_red_tail`` - perform tail reductions (default: ``True``)

        - ``opt_red_tail_deg_growth`` - (default: ``True``)

        - ``opt_brutal_reductions`` - (default: ``True``)

        OTHER ATTRIBUTES:

        - ``leading_terms`` - all leading terms of generators

        - ``minimal_leading_terms`` - the reduced set of leading terms

        - ``monomials`` -

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.opt_red_tail = True
            sage: red.add_generator(x + y + 1)
            sage: red.add_generator(x*y + y)
            sage: red.add_generator(y*z + z)

            sage: red.opt_ll
            False

            sage: red.opt_red_tail
            True

            sage: red.opt_brutal_reductions
            True

            sage: red.opt_red_tail_deg_growth
            True

            sage: red.leading_terms
            {{x,y}, {x}, {y,z}}
            sage: red.minimal_leading_terms
            {{x}, {y,z}}
        """
        cdef PBRedStrategy* strat = self._strat.get()
        if name == 'opt_ll':
            return strat.optLL
        elif name == 'opt_red_tail':
            return strat.optRedTail
        elif name == 'opt_brutal_reductions':
            return strat.optBrutalReductions
        elif name == 'opt_red_tail_deg_growth':
            return strat.optRedTailDegGrowth

        elif name == 'leading_terms':
            return new_BS_from_PBSet(strat.leadingTerms, self._parent)
        elif name == 'minimal_leading_terms':
            return new_BS_from_PBSet(strat.minimalLeadingTerms, self._parent)

        elif name == 'monomials':
            return new_BS_from_PBSet(strat.monomials, self._parent)

        raise AttributeError(name)

    def __setattr__(self, name, val):
        cdef PBRedStrategy* strat = self._strat.get()
        if name == 'opt_red_tail':
            strat.optRedTail = val
        elif name == 'opt_ll':
            strat.optLL = val
        elif name == 'opt_brutal_reductions':
            strat.optBrutalReductions = val
        elif name == 'opt_red_tail_deg_growth':
            strat.optRedTailDegGrowth = val
        else:
            raise AttributeError(name)

    def __len__(self):
        """
        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: red = ReductionStrategy(B)
            sage: red.opt_red_tail = True
            sage: red.add_generator(x + y + 1)
            sage: red.add_generator(x*y + y)
            sage: red.add_generator(y*z + z)
            sage: len(red)
            3
        """
        return deref(self._strat).size()

    def __getitem__(self, Py_ssize_t i):
        cdef PBPoly t
        if i < 0 or <size_t>i >= deref(self._strat).size():
            raise IndexError
        return BooleanPolynomialEntry(new_BP_from_PBPoly(self._parent,
                deref(self._strat)[i].p))


cdef class BooleanPolynomialEntry:
    def __init__(self, p):
        self.p = <BooleanPolynomial?>p


cdef class FGLMStrategy:
    """
    Strategy object for the FGLM algorithm to translate from one
    Groebner basis with respect to a term ordering A to another
    Groebner basis with respect to a term ordering B.
    """
    def __init__(self, from_ring, to_ring, BooleanPolynomialVector vec):
        """
        Execute the FGLM algorithm.

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: x > y > z
            True
            sage: old_ring  = B
            sage: new_ring = B.clone(ordering=lp)
            sage: new_ring.gen(0) > new_ring.gen(1) > new_ring.gen(2)
            True
            sage: new_ring.gen(2) > new_ring.gen(1) > new_ring.gen(0)
            False
            sage: ideal = BooleanPolynomialVector([x+z, y+z])
            sage: FGLMStrategy(old_ring, new_ring, ideal)
            <sage.rings.polynomial.pbori.FGLMStrategy object at 0x...>

        Check that :trac:`13883` is fixed::

            sage: nonreduced = BooleanPolynomialVector([x+z, x+y])
            sage: FGLMStrategy(old_ring, new_ring, nonreduced) # optional - debug
            Traceback (most recent call last):
            ...
            RuntimeError...

        """
        cdef BooleanPolynomialRing _from_ring, _to_ring

        if isinstance(from_ring, BooleanPolynomialRing):
            _from_ring = <BooleanPolynomialRing>from_ring
        elif isinstance(from_ring.ring, BooleanPolynomialRing):
            _from_ring = <BooleanPolynomialRing>from_ring.ring
        else:
            raise TypeError("from_ring has wrong type %s" % (type(from_ring),))

        if isinstance(to_ring, BooleanPolynomialRing):
            _to_ring = <BooleanPolynomialRing>to_ring
        elif isinstance(to_ring.ring, BooleanPolynomialRing):
            _to_ring = <BooleanPolynomialRing>to_ring.ring
        else:
            raise TypeError("to_ring has wrong type %s" % (type(to_ring),))
        cdef PBFGLMStrategy* strat = new PBFGLMStrategy(_from_ring._pbring, _to_ring._pbring, vec._vec)
        self._strat = unique_ptr[PBFGLMStrategy](strat)
        self._parent = to_ring

    def main(self):
        """
        Execute the FGLM algorithm.

        EXAMPLES::

            sage: from brial import *
            sage: B.<x,y,z> = BooleanPolynomialRing()
            sage: ideal = BooleanPolynomialVector([x+z, y+z])
            sage: list(ideal)
            [x + z, y + z]
            sage: old_ring = B
            sage: new_ring = B.clone(ordering=dp_asc)
            sage: list(FGLMStrategy(old_ring, new_ring, ideal).main())
            [y + x, z + x]
        """
        return new_BPV_from_PBPolyVector(self._parent, deref(self._strat).main())


cdef class GroebnerStrategy:
    """
    A Groebner strategy is the main object to control the strategy for
    computing Groebner bases.

    .. NOTE::

      This class is mainly used internally.
    """
    def __init__(self, param):
        """

        INPUT:

        - ``param`` - either ``None`` or a :class:`GroebnerStrategy`
          object.

        EXAMPLES::

            sage: from brial import GroebnerStrategy
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: G = GroebnerStrategy(B)
            sage: H = GroebnerStrategy(G)
            sage: del G
            sage: del H
        """
        if isinstance(param, GroebnerStrategy):
            self._strat = (<GroebnerStrategy>param)._strat
            self._parent = (<GroebnerStrategy>param)._parent
        elif isinstance(param, BooleanPolynomialRing):
            self._strat = make_shared[PBGBStrategy]((<BooleanPolynomialRing>param)._pbring)
            self._parent = param
        else:
            raise ValueError("Cannot generate GroebnerStrategy from %s." %
                             type(param))

        self.reduction_strategy = ReductionStrategy(self._parent)
        self.reduction_strategy._strat = shared_ptr_alias_PBGBStrategy[PBRedStrategy](self._strat, &deref(self._strat).generators)

    def add_generator_delayed(self, BooleanPolynomial p):
        """
        Add a new generator but do not perform interreduction
        immediatly.

        INPUT:

        - ``p`` - a polynomial

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: gbs = GroebnerStrategy(B)
            sage: gbs.add_generator(a + b)
            sage: list(gbs)
            [a + b]
            sage: gbs.add_generator_delayed(a + c)
            sage: list(gbs)
            [a + b]

            sage: list(gbs.all_generators())
            [a + b, a + c]
        """
        if p._pbpoly.isZero():
            raise ValueError("zero generators not allowed.")
        deref(self._strat).addGeneratorDelayed(p._pbpoly)

    def add_generator(self, BooleanPolynomial p):
        """
        Add a new generator.

        INPUT:

        - ``p`` - a polynomial

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: gbs = GroebnerStrategy(B)
            sage: gbs.add_generator(a + b)
            sage: list(gbs)
            [a + b]
            sage: gbs.add_generator(a + c)
            Traceback (most recent call last):
            ...
            ValueError: strategy already contains a polynomial with same lead
        """
        if p._pbpoly.isZero():
            raise ValueError("zero generators not allowed.")
        if deref(self._strat).generators.leadingTerms.owns(p._pbpoly.lead()):
            raise ValueError("strategy already contains a polynomial with same lead")
        deref(self._strat).generators.addGenerator(p._pbpoly)

    def add_as_you_wish(self, BooleanPolynomial p):
        """
        Add a new generator but let the strategy object decide whether
        to perform immediate interreduction.

        INPUT:

        - ``p`` - a polynomial

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: gbs = GroebnerStrategy(B)
            sage: gbs.add_as_you_wish(a + b)
            sage: list(gbs)
            [a + b]
            sage: gbs.add_as_you_wish(a + c)

        Note that nothing happened immediatly but that the generator
        was indeed added::

            sage: list(gbs)
            [a + b]

            sage: gbs.symmGB_F2()
            sage: list(gbs)
            [a + c, b + c]
        """
        if p._pbpoly.isZero():
            raise ValueError("zero generators not allowed.")
        deref(self._strat).addAsYouWish(p._pbpoly)

    def implications(self, i):
        """
        Compute "useful" implied polynomials of ``i``-th generator,
        and add them to the strategy, if it finds any.

        INPUT:

        - ``i`` - an index
        """
        cdef PBGBStrategy* strat = self._strat.get()
        strat.addNonTrivialImplicationsDelayed(strat.generators[i])

    def clean_top_by_chain_criterion(self):
        deref(self._strat).cleanTopByChainCriterion()

    def symmGB_F2(self):
        """
        Compute a Groebner basis for the generating system.

        .. NOTE::

          This implementation is out of date, but it will revived at
          some point in time. Use the ``groebner_basis()`` function
          instead.
        """
        deref(self._strat).symmGB_F2()

    def contains_one(self):
        """
        Return ``True`` if 1 is in the generating system.

        EXAMPLES:

        We construct an example which contains ``1`` in the ideal
        spanned by the generators but not in the set of generators::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import GroebnerStrategy
            sage: gb = GroebnerStrategy(B)
            sage: gb.add_generator(a*c + a*f + d*f + d + f)
            sage: gb.add_generator(b*c + b*e + c + d + 1)
            sage: gb.add_generator(a*f + a + c + d + 1)
            sage: gb.add_generator(a*d + a*e + b*e + c + f)
            sage: gb.add_generator(b*d + c + d*f + e + f)
            sage: gb.add_generator(a*b + b + c*e + e + 1)
            sage: gb.add_generator(a + b + c*d + c*e + 1)
            sage: gb.contains_one()
            False

        Still, we have that::

            sage: from brial import groebner_basis
            sage: groebner_basis(gb)
            [1]
        """
        return deref(self._strat).containsOne()

    def faugere_step_dense(self, BooleanPolynomialVector v):
        """
        Reduces a vector of polynomials using linear algebra.

        INPUT:

        - ``v`` - a boolean polynomial vector

        EXAMPLES::

            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import GroebnerStrategy
            sage: gb = GroebnerStrategy(B)
            sage: gb.add_generator(a*c + a*f + d*f + d + f)
            sage: gb.add_generator(b*c + b*e + c + d + 1)
            sage: gb.add_generator(a*f + a + c + d + 1)
            sage: gb.add_generator(a*d + a*e + b*e + c + f)
            sage: gb.add_generator(b*d + c + d*f + e + f)
            sage: gb.add_generator(a*b + b + c*e + e + 1)
            sage: gb.add_generator(a + b + c*d + c*e + 1)

            sage: from brial import BooleanPolynomialVector
            sage: V= BooleanPolynomialVector([b*d, a*b])
            sage: list(gb.faugere_step_dense(V))
            [b + c*e + e + 1, c + d*f + e + f]
        """
        return new_BPV_from_PBPolyVector(self._parent,
                deref(self._strat).faugereStepDense(v._vec))

    def minimalize(self):
        """
        Return a vector of all polynomials with minimal leading terms.

        .. NOTE::

           Use this function if strat contains a GB.
        """
        return new_BPV_from_PBPolyVector(self._parent,
                deref(self._strat).minimalize())

    def minimalize_and_tail_reduce(self):
        """
        Return a vector of all polynomials with minimal leading terms
        and do tail reductions.

        .. NOTE::

          Use that if strat contains a GB and you want a reduced GB.
        """
        return new_BPV_from_PBPolyVector(self._parent,
                deref(self._strat).minimalizeAndTailReduce())

    def npairs(self):
        return deref(self._strat).npairs()

    def top_sugar(self):
        return pairs_top_sugar(deref(self._strat))

    def some_spolys_in_next_degree(self, n):
        return new_BPV_from_PBPolyVector(self._parent,
                someNextDegreeSpolys(deref(self._strat), n))

    def all_spolys_in_next_degree(self):
        return new_BPV_from_PBPolyVector(self._parent,
                nextDegreeSpolys(deref(self._strat)))

    def small_spolys_in_next_degree(self, double f, int n):
        return new_BPV_from_PBPolyVector(self._parent,
                small_next_degree_spolys(deref(self._strat), f, n))

    def ll_reduce_all(self):
        """
        Use the built-in ll-encoded :class:`BooleSet` of polynomials
        with linear lexicographical leading term, which coincides with
        leading term in current ordering, to reduce the tails of all
        polynomials in the strategy.
        """
        deref(self._strat).llReduceAll()

    def next_spoly(self):
        return new_BP_from_PBPoly(self._parent,
                deref(self._strat).nextSpoly())

    def all_generators(self):
        """
        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: gbs = GroebnerStrategy(B)
            sage: gbs.add_as_you_wish(a + b)
            sage: list(gbs)
            [a + b]
            sage: gbs.add_as_you_wish(a + c)

            sage: list(gbs)
            [a + b]

            sage: list(gbs.all_generators())
            [a + b, a + c]
        """
        return new_BPV_from_PBPolyVector(self._parent,
                deref(self._strat).allGenerators())

    def suggest_plugin_variable(self):
        return deref(self._strat).suggestPluginVariable()

    def variable_has_value(self, int v):
        """
        Computes, whether there exists some polynomial of the form
        `v+c` in the Strategy -- where ``c`` is a constant -- in the
        list of generators.

        INPUT:

        - ``v`` - the index of a variable

        EXAMPLES::
            sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
            sage: from brial import GroebnerStrategy
            sage: gb = GroebnerStrategy(B)
            sage: gb.add_generator(a*c + a*f + d*f + d + f)
            sage: gb.add_generator(b*c + b*e + c + d + 1)
            sage: gb.add_generator(a*f + a + c + d + 1)
            sage: gb.add_generator(a*d + a*e + b*e + c + f)
            sage: gb.add_generator(b*d + c + d*f + e + f)
            sage: gb.add_generator(a*b + b + c*e + e + 1)
            sage: gb.variable_has_value(0)
            False

            sage: from brial import groebner_basis
            sage: g = groebner_basis(gb)
            sage: list(g)
            [a, b + 1, c + 1, d, e + 1, f]

            sage: gb = GroebnerStrategy(B)
            sage: _ = [gb.add_generator(f) for f in g]
            sage: gb.variable_has_value(0)
            True
        """
        return deref(self._strat).variableHasValue(v)

    def nf(self, BooleanPolynomial p):
        """
        Compute the normal form of ``p`` with respect to the
        generating set.

        INPUT:

        - ``p`` - a boolean polynomial

        EXAMPLES::

            sage: P = PolynomialRing(GF(2),10, 'x')
            sage: B = BooleanPolynomialRing(10,'x')
            sage: I = sage.rings.ideal.Cyclic(P)
            sage: I = B.ideal([B(f) for f in I.gens()])
            sage: gb = I.groebner_basis()

            sage: from brial import GroebnerStrategy

            sage: G = GroebnerStrategy(B)
            sage: _ = [G.add_generator(f) for f in gb]
            sage: G.nf(gb[0])
            0
            sage: G.nf(gb[0] + 1)
            1
            sage: G.nf(gb[0]*gb[1])
            0
            sage: G.nf(gb[0]*B.gen(1))
            0

        .. NOTE::

          The result is only canonical if the generating set is a
          Groebner basis.

        """
        return new_BP_from_PBPoly(self._parent, deref(self._strat).nf(p._pbpoly))

    def select(self, BooleanMonomial m):
        """
        Return the index of the generator which can reduce the
        monomial ``m``.

        INPUT:

        - ``m`` - a :class:`BooleanMonomial`

        EXAMPLES::

            sage: B.<a,b,c,d,e> = BooleanPolynomialRing()
            sage: f = B.random_element()
            sage: g = B.random_element()
            sage: from brial import GroebnerStrategy
            sage: strat = GroebnerStrategy(B)
            sage: strat.add_generator(f)
            sage: strat.add_generator(g)
            sage: strat.select(f.lm())
            0
            sage: strat.select(g.lm())
            1
            sage: strat.select(e.lm())
            -1
        """
        return deref(self._strat).generators.select1(m._pbmonom)

    def __len__(self):
        """
        Return the number of generators.

        EXAMPLES::

            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: from brial import GroebnerStrategy

            sage: G = GroebnerStrategy(B)
            sage: G.add_as_you_wish(a)
            sage: len(G)
            1
            sage: G.add_as_you_wish(b)
            sage: len(G)
            2
            sage: G.add_as_you_wish(b + 1)
            sage: len(G)
            2
        """
        return deref(self._strat).generators.size()

    def __getitem__(self, Py_ssize_t i):
        cdef PBPoly t
        if i < 0 or <size_t>i >= deref(self._strat).generators.size():
            raise IndexError
        return new_BP_from_PBPoly(self._parent, deref(self._strat).generators[i].p)

    def __getattr__(self, name):
        cdef PBGBStrategy* strat = self._strat.get()
        if name == 'enabled_log':
            return strat.enabledLog
        elif name == 'opt_lazy':
            return strat.optLazy
        elif name == 'opt_exchange':
            return strat.optExchange
        elif name == 'opt_allow_recursion':
            return strat.optAllowRecursion
        elif name == 'opt_linear_algebra_in_last_block':
            return strat.optLinearAlgebraInLastBlock
        elif name == 'opt_modified_linear_algebra':
            return strat.optModifiedLinearAlgebra
        elif name == 'opt_draw_matrices':
            return strat.optDrawMatrices
        elif name == '"opt_red_by_reduced':
            return strat.reduceByTailReduced
        elif name == 'chain_criterions':
            return strat.chainCriterions
        elif name == 'variable_chain_criterions':
            return strat.variableChainCriterions
        elif name == 'easy_product_criterions':
            return strat.easyProductCriterions
        elif name == 'extended_product_criterions':
            return strat.extendedProductCriterions
        elif name == 'matrix_prefix':
            return strat.matrixPrefix.c_str()

        raise AttributeError(name)

    def __setattr__(self, name, val):
        cdef PBGBStrategy* strat = self._strat.get()
        if name == 'enabled_log':
            strat.enabledLog = val
        elif name == 'opt_lazy':
            strat.optLazy = val
        elif name == 'opt_exchange':
            strat.optExchange = val
        elif name == 'opt_allow_recursion':
            strat.optAllowRecursion = val
        elif name == 'opt_linear_algebra_in_last_block':
            strat.optLinearAlgebraInLastBlock = val
        elif name == 'opt_modified_linear_algebra':
            strat.optModifiedLinearAlgebra = val
        elif name == 'opt_red_by_reduced':
            strat.reduceByTailReduced = val
        elif name == 'opt_draw_matrices':
            strat.optDrawMatrices = val
        elif name == 'matrix_prefix':
            val = str_to_bytes(val)
            strat.matrixPrefix = std_string(<char*>val)
        elif name == 'redByReduced': # working around a bug in PolyBoRi 0.6
            strat.reduceByTailReduced = val
        else:
            raise AttributeError(name)


cdef class BooleanMulAction(Action):
    cpdef _act_(self, g, x):
        """
        EXAMPLES::

            sage: from brial import BooleanMonomialMonoid
            sage: P.<x,y,z> = BooleanPolynomialRing(3)
            sage: M = BooleanMonomialMonoid(P)
            sage: x = M(x); xy = M(x*y); z=M(z)
            sage: x*1  # indirect doctest
            x
            sage: 1*x
            x
            sage: x*int(1)
            x
            sage: int(1)*x
            x
            sage: 0*x
            0
            sage: x*2
            0
        """
        return x if (g % 2) else GF(2)(0)


cdef inline CCuddNavigator new_CN_from_PBNavigator(PBNavigator juice,
                                                   Py_ssize_t* pbind):
    """
    Construct a new CCuddNavigator
    """
    cdef CCuddNavigator n
    n = <CCuddNavigator>CCuddNavigator.__new__(CCuddNavigator)
    n._pbnav = juice
    n._pbind = pbind
    return n

cdef class VariableBlock:
    def __init__(self, int size, int start_index, int offset, bint reverse,
                 BooleanPolynomialRing ring):
        self._ring = ring
        self._block = new PBVarBlock(size, start_index, offset, reverse,
                                     ring._pbring)

    def __dealloc__(self):
        self._ring = None
        del self._block

    def __call__(self, int i):
        return new_BM_from_PBVar(self._ring._monom_monoid,
                                 self._ring, deref(self._block)(i))


def add_up_polynomials(BooleanPolynomialVector v, BooleanPolynomial init):
    """
    Add up all entries in the vector ``v``.

    INPUT:

    - ``v`` - a vector of boolean polynomials

    EXAMPLES::

        sage: from brial import *
        sage: B.<a,b,c,d> = BooleanPolynomialRing()
        sage: v = BooleanPolynomialVector()
        sage: l = [B.random_element() for _ in range(5)]
        sage: _ = [v.append(e) for e in l]
        sage: add_up_polynomials(v, B.zero())
        a*d + b*c + b*d + c + 1
        sage: sum(l)
        a*d + b*c + b*d + c + 1
    """
    return new_BP_from_PBPoly(v._parent, pb_add_up_polynomials(v._vec, init._pbpoly))


def nf3(ReductionStrategy s, BooleanPolynomial p, BooleanMonomial m):
    return new_BP_from_PBPoly(s._parent,
            pb_nf3(deref(s._strat), p._pbpoly, m._pbmonom))


def red_tail(ReductionStrategy s, BooleanPolynomial p):
    """
    Perform tail reduction on ``p`` using the generators of ``s``.

    INPUT:

    - ``s`` - a reduction strategy
    - ``p`` - a polynomial

    EXAMPLES::

        sage: from brial import *
        sage: B.<x,y,z> = BooleanPolynomialRing()
        sage: red = ReductionStrategy(B)
        sage: red.add_generator(x + y + 1)
        sage: red.add_generator(y*z + z)
        sage: red_tail(red,x)
        x
        sage: red_tail(red,x*y + x)
        x*y + y + 1
    """
    return new_BP_from_PBPoly(p._parent, pb_red_tail(deref(s._strat), p._pbpoly))


def map_every_x_to_x_plus_one(BooleanPolynomial p):
    """
    Map every variable ``x_i`` in this polynomial to ``x_i + 1``.

    EXAMPLES::

        sage: B.<a,b,z> = BooleanPolynomialRing(3)
        sage: f = a*b + z + 1; f
        a*b + z + 1
        sage: from brial import map_every_x_to_x_plus_one
        sage: map_every_x_to_x_plus_one(f)
        a*b + a + b + z + 1
        sage: f(a+1,b+1,z+1)
        a*b + a + b + z + 1
    """

    return new_BP_from_PBPoly(p._parent,
            pb_map_every_x_to_x_plus_one(p._pbpoly))


def zeros(pol, BooleSet s):
    """
    Return a ``BooleSet`` encoding on which points from ``s`` the
    polynomial ``pol`` evaluates to zero.

    INPUT:

    - ``pol`` - a boolean polynomial

    - ``s`` - a set of points encoded as a ``BooleSet``

    EXAMPLES::

        sage: B.<a,b,c,d> = BooleanPolynomialRing(4)
        sage: f = a*b + a*c + d + b

    Now we create a set of points::

        sage: s = a*b + a*b*c + c*d + b*c
        sage: s = s.set(); s
        {{a,b,c}, {a,b}, {b,c}, {c,d}}

    This encodes the points (1,1,1,0), (1,1,0,0), (0,0,1,1) and
    (0,1,1,0). But of these only (1,1,0,0) evaluates to zero.::

        sage: from brial import zeros
        sage: zeros(f,s)
        {{a,b}}

    For comparison we work with tuples::

        sage: f.zeros_in([(1,1,1,0), (1,1,0,0), (0,0,1,1), (0,1,1,0)])
        ((1, 1, 0, 0),)

    """
    cdef PBPoly p
    if isinstance(pol, BooleanPolynomial):
        p = (<BooleanPolynomial>pol)._pbpoly
    elif isinstance(pol, BooleanMonomial):
        p = PBBoolePolynomial((<BooleanMonomial>pol)._pbmonom)
    else:
        raise TypeError("Argument 'p' has incorrect type (expected BooleanPolynomial or BooleanMonomial, got %s)" % type(pol))
    return new_BS_from_PBSet(pb_zeros(p, s._pbset), s._ring)


def interpolate(zero, one):
    r"""
    Interpolate a polynomial evaluating to zero on ``zero`` and to
    one on ``ones``.

    INPUT:

    - ``zero`` - the set of zero

    - ``one`` - the set of ones

    EXAMPLES::

        sage: B = BooleanPolynomialRing(4,"x0,x1,x2,x3")
        sage: x = B.gen
        sage: from brial.interpolate import *
        sage: V=(x(0)+x(1)+x(2)+x(3)+1).set()

        sage: V
        {{x0}, {x1}, {x2}, {x3}, {}}

        sage: f=x(0)*x(1)+x(1)+x(2)+1
        sage: nf_lex_points(f,V)
        x1 + x2 + 1

        sage: z=f.zeros_in(V)
        sage: z
        {{x1}, {x2}}

        sage: o=V.diff(z)
        sage: o
        {{x0}, {x3}, {}}

        sage: interpolate(z,o)
        x0*x1*x2 + x0*x1 + x0*x2 + x1*x2 + x1 + x2 + 1
    """
    cdef PBSet z, o
    cdef BooleanPolynomialRing ring
    if isinstance(zero, BooleSet):
        z = (<BooleSet>zero)._pbset
        ring = (<BooleSet>zero)._ring
    elif isinstance(zero, BooleanPolynomial):
        z = (<BooleanPolynomial>zero)._pbpoly.set()
        ring = (<BooleanPolynomial>zero)._parent
    else:
        raise TypeError("Argument 'zero' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(zero))
    if isinstance(one, BooleSet):
        o = (<BooleSet>one)._pbset
    elif isinstance(one, BooleanPolynomial):
        o = (<BooleanPolynomial>one)._pbpoly.set()
    else:
        raise TypeError("Argument 'one' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(one))
    return new_BP_from_PBPoly(ring, pb_interpolate(z, o))


def interpolate_smallest_lex(zero, one):
    r"""
    Interpolate the lexicographical smallest polynomial evaluating to
    zero on ``zero`` and to one on ``ones``.

    INPUT:

    - ``zero`` - the set of zeros

    - ``one`` - the set of ones

    EXAMPLES:

    Let V be a set of points in `\GF{2}^n` and f a Boolean
    polynomial. V can be encoded as a ``BooleSet``. Then we are
    interested in the normal form of f against the vanishing ideal of
    V : I(V).

    It turns out, that the computation of the normal form can be done
    by the computation of a minimal interpolation polynomial, which
    takes the same values as f on V::


        sage: B = BooleanPolynomialRing(4,"x0,x1,x2,x3")
        sage: x = B.gen
        sage: from brial.interpolate import *
        sage: V=(x(0)+x(1)+x(2)+x(3)+1).set()

    We take V = {e0,e1,e2,e3,0}, where ei describes the i-th unit
    vector. For our considerations it does not play any role, if we
    suppose V to be embedded in `\GF{2}^4` or a vector space of higher
    dimension::

        sage: V
        {{x0}, {x1}, {x2}, {x3}, {}}

        sage: f=x(0)*x(1)+x(1)+x(2)+1
        sage: nf_lex_points(f,V)
        x1 + x2 + 1

    In this case, the normal form of f w.r.t. the vanishing ideal of V
    consists of all terms of f with degree smaller or equal to 1.

    It can be easily seen, that this polynomial forms the same
    function on V as f. In fact, our computation is equivalent to the
    direct call of the interpolation function
    ``interpolate_smallest_lex``, which has two arguments: the set of
    interpolation points mapped to zero and the set of interpolation
    points mapped to one::

        sage: z=f.zeros_in(V)
        sage: z
        {{x1}, {x2}}

        sage: o=V.diff(z)
        sage: o
        {{x0}, {x3}, {}}

        sage: interpolate_smallest_lex(z,o)
        x1 + x2 + 1
    """
    cdef PBSet z, o
    if isinstance(zero, BooleSet):
        z = (<BooleSet>zero)._pbset
    elif isinstance(zero, BooleanPolynomial):
        z = (<BooleanPolynomial>zero)._pbpoly.set()
    else:
        raise TypeError("Argument 'zero' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(zero))
    if isinstance(one, BooleSet):
        o = (<BooleSet>one)._pbset
    elif isinstance(one, BooleanPolynomial):
        o = (<BooleanPolynomial>one)._pbpoly.set()
    else:
        raise TypeError("Argument 'one' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(one))

    return new_BP_from_PBPoly(zero.ring(), pb_interpolate_smallest_lex(z, o))


def contained_vars(BooleSet m):
    return new_BS_from_PBSet(pb_contained_variables_cudd_style(m._pbset),
            m._ring)


def mod_var_set(BooleSet a, BooleSet v):
    return new_BS_from_PBSet(pb_mod_var_set(a._pbset, v._pbset), a._ring)


def mult_fact_sim_C(BooleanPolynomialVector v, BooleanPolynomialRing ring):
    return new_BP_from_PBPoly(v._parent, pb_mult_fast_sim(v._vec, ring._pbring))


def recursively_insert(CCuddNavigator n, int ind, BooleSet m):
    cdef PBSet b
    cdef BooleanPolynomialRing ring = m.ring()
    b = pb_recursively_insert(n._pbnav, ring.pbind[ind], m._pbset)
    return new_BS_from_PBSet(b, m._ring)


def ll_red_nf_redsb(p, BooleSet reductors):
    """
    Redude the polynomial ``p`` by the set of ``reductors`` with
    linear leading terms. It is assumed that the set ``reductors`` is
    a reduced Groebner basis.

    INPUT:

    - ``p`` - a boolean polynomial

    - ``reductors`` - a boolean set encoding a reduced Groebner basis
      with linear leading terms.

    EXAMPLES::

        sage: from brial import ll_red_nf_redsb
        sage: B.<a,b,c,d> = BooleanPolynomialRing()
        sage: p = a*b + c + d + 1
        sage: f,g  = a + c + 1, b + d + 1
        sage: reductors = f.set().union( g.set() )
        sage: ll_red_nf_redsb(p, reductors)
        b*c + b*d + c + d + 1
    """
    cdef PBPoly t
    cdef PBPoly res
    cdef BooleanPolynomialRing parent
    if isinstance(p, BooleSet):
        t = PBBoolePolynomial((<BooleSet>p)._pbset)
        parent = (<BooleSet>p)._ring
    elif isinstance(p, BooleanPolynomial):
        t = (<BooleanPolynomial>p)._pbpoly
        parent = (<BooleanPolynomial>p)._parent
    elif isinstance(p, BooleanMonomial):
        t = PBBoolePolynomial((<BooleanMonomial>p)._pbmonom)
        parent = (<BooleanMonomial>p)._ring
    else:
        raise TypeError("Argument 'p' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(p))

    res = pb_ll_red_nf(t, reductors._pbset)

    return new_BP_from_PBPoly(parent, res)


def ll_red_nf_noredsb(BooleanPolynomial p, BooleSet reductors):
    """
    Redude the polynomial ``p`` by the set of ``reductors`` with
    linear leading terms.

    INPUT:

    - ``p`` - a boolean polynomial

    - ``reductors`` - a boolean set encoding a Groebner basis with
      linear leading terms.

    EXAMPLES::

        sage: from brial import ll_red_nf_noredsb
        sage: B.<a,b,c,d> = BooleanPolynomialRing()
        sage: p = a*b + c + d + 1
        sage: f,g  = a + c + 1, b + d + 1
        sage: reductors = f.set().union( g.set() )
        sage: ll_red_nf_noredsb(p, reductors)
        b*c + b*d + c + d + 1
    """
    cdef PBPoly t
    t = pb_ll_red_nf_noredsb(p._pbpoly, reductors._pbset)
    return new_BP_from_PBPoly(p._parent, t)


def ll_red_nf_noredsb_single_recursive_call(BooleanPolynomial p, BooleSet reductors):
    """
    Redude the polynomial ``p`` by the set of ``reductors`` with
    linear leading terms.

    :func:`ll_red_nf_noredsb_single_recursive` call has the same
    specification as :func:`ll_red_nf_noredsb`, but a different
    implementation: It is very sensitive to the ordering of variables,
    however it has the property, that it needs just one recursive
    call.

    INPUT:

    - ``p`` - a boolean polynomial

    - ``reductors`` - a boolean set encoding a Groebner basis with
      linear leading terms.

    EXAMPLES::

        sage: from brial import ll_red_nf_noredsb_single_recursive_call
        sage: B.<a,b,c,d> = BooleanPolynomialRing()
        sage: p = a*b + c + d + 1
        sage: f,g  = a + c + 1, b + d + 1
        sage: reductors = f.set().union( g.set() )
        sage: ll_red_nf_noredsb_single_recursive_call(p, reductors)
        b*c + b*d + c + d + 1
    """
    cdef PBPoly t
    t = pb_ll_red_nf_noredsb_single_recursive_call(p._pbpoly, reductors._pbset)
    return new_BP_from_PBPoly(p._parent, t)


def mod_mon_set(BooleSet a_s, BooleSet v_s):
    cdef PBSet b
    b = pb_mod_mon_set(a_s._pbset, v_s._pbset)
    return new_BS_from_PBSet(b, a_s._ring)


def parallel_reduce(BooleanPolynomialVector inp, GroebnerStrategy strat,
                                    int average_steps, double delay_f):
    return new_BPV_from_PBPolyVector(inp._parent,
        pb_parallel_reduce(inp._vec, deref(strat._strat), average_steps, delay_f))


def if_then_else(root, a, b):
    """
    The opposite of navigating down a ZDD using navigators is to
    construct new ZDDs in the same way, namely giving their else- and
    then-branch as well as the index value of the new node.

    INPUT:

    -  ``root`` - a variable

    - ``a`` - the if branch, a ``BooleSet`` or a ``BoolePolynomial``

    - ``b`` - the else branch, a ``BooleSet`` or a ``BoolePolynomial``

    EXAMPLES::

        sage: from brial import if_then_else
        sage: B = BooleanPolynomialRing(6,'x')
        sage: x0,x1,x2,x3,x4,x5 = B.gens()
        sage: f0 = x2*x3+x3
        sage: f1 = x4
        sage: if_then_else(x1, f0, f1)
        {{x1,x2,x3}, {x1,x3}, {x4}}

    ::

        sage: if_then_else(x1.lm().index(),f0,f1)
        {{x1,x2,x3}, {x1,x3}, {x4}}

    ::

        sage: if_then_else(x5, f0, f1)
        Traceback (most recent call last):
        ...
        IndexError: index of root must be less than the values of roots of the branches.
    """
    cdef PBSet a_set, b_set
    cdef PBSet res
    cdef BooleanPolynomialRing ring
    if isinstance(b, BooleSet):
        b_set = (<BooleSet>b)._pbset
        ring = (<BooleSet>b)._ring
    elif isinstance(b, BooleanPolynomial):
        b_set = (<BooleanPolynomial>b)._pbpoly.set()
        ring = (<BooleanPolynomial>b)._parent
    else:
        raise TypeError("Argument 'b' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(b))

    if isinstance(a, BooleSet):
        a_set = (<BooleSet>a)._pbset
    elif isinstance(a, BooleanPolynomial):
        a_set = (<BooleanPolynomial>a)._pbpoly.set()
    else:
        raise TypeError("Argument 'a' has incorrect type (expected BooleSet or BooleanPolynomial, got %s)" % type(a))

    try:
        root = int(root)
    except TypeError:
        if isinstance(root, BooleanPolynomial):
            if len(root) == 1:
                root = root.lm()
            else:
                raise TypeError("Only variables are acceptable as root.")
        if isinstance(root, BooleanMonomial):
            if len(root) == 1:
                root = root.index()
            else:
                raise TypeError("Only variables are acceptable as root.")

        if not isinstance(root, int):
            raise TypeError("Only variables are acceptable as root.")

    cdef Py_ssize_t* pbind = ring.pbind
    root = ring.pbind[root]

    if (root >= a_set.navigation().value()) or (root >= b_set.navigation().value()):
        raise IndexError("index of root must be less than "
                         "the values of roots of the branches.")

    res = PBBooleSet(root, a_set.navigation(),
                     b_set.navigation(), ring._pbring)
    return new_BS_from_PBSet(res, ring)


def top_index(s):
    """
    Return the highest index in the parameter ``s``.

    INPUT:

    - ``s`` - ``BooleSet``, ``BooleMonomial``, ``BoolePolynomial``

    EXAMPLES::

        sage: B.<x,y,z> = BooleanPolynomialRing(3)
        sage: from brial import top_index
        sage: top_index(x.lm())
        0
        sage: top_index(y*z)
        1
        sage: top_index(x + 1)
        0
    """
    cdef  Py_ssize_t idx = -1
    if isinstance(s, BooleSet):
        idx = (<BooleSet>s)._pbset.navigation().value()
    elif isinstance(s, BooleanMonomial):
        idx = (<BooleanMonomial>s)._pbmonom.firstIndex()
    elif isinstance(s, BooleanPolynomial):
        idx = (<BooleanPolynomial>s)._pbpoly.navigation().value()
    else:
        raise TypeError("Argument 's' has incorrect type (expected BooleSet, BooleanMonomial or BooleanPolynomial, got %s)" % type(s))
    return (<BooleanPolynomialRing>s.ring()).pbind[idx]


cdef long PBRing_identifier(PBRing pbring):

    cdef long _hash = pbring.hash() ^ hash(pbring.ordering().getOrderCode())

    cdef PBBlockIter start  = pbring.ordering().blockBegin()
    cdef PBBlockIter finish = pbring.ordering().blockEnd()
    while start != finish:
        _hash ^= start.dereference()
        start.increment()

    return _hash


cdef object TermOrder_from_PBRing(PBRing _ring):
    cdef int n = _ring.nVariables()
    pb_base_order_code = _ring.ordering().getBaseOrderCode()
    order_str = inv_order_dict[pb_base_order_code]

    cdef PBBlockIter it = _ring.ordering().blockBegin()
    cdef int ctr = 0
    cdef int value = 0
    T = None

    while it != _ring.ordering().blockEnd():
        value = min(it.dereference(), n)
        T = TermOrder(order_str, value-ctr, force=True) + T
        ctr = value
        it.increment()

    if T is None:
        T = TermOrder(order_str, force=True)

    return T

cdef BooleanPolynomialRing BooleanPolynomialRing_from_PBRing(PBRing _ring):
    """
    Get BooleanPolynomialRing from C++-implementation
    """
    cdef int i,j
    cdef BooleanPolynomialRing self = BooleanPolynomialRing.__new__(BooleanPolynomialRing)

    cdef int n = _ring.nVariables()

    self.pbind = <Py_ssize_t*>sig_malloc(n*sizeof(Py_ssize_t))

    T = TermOrder_from_PBRing(_ring)

    # pbdp and pbblock_dp cannot occur here
    for i from 0 <= i < n:
        self.pbind[i] = i

    names = []
    for i in range(n):
        name = char_to_str(_ring.getVariableName(i))
        name = name.replace("(","").replace(")","")
        names.append(name)

    self._pbring = _ring

    MPolynomialRing_base.__init__(self, GF(2), n, names, T)

    self._zero_element = new_BP(self)
    (<BooleanPolynomial>self._zero_element)._pbpoly = PBBoolePolynomial(0, self._pbring)
    self._one_element  = new_BP(self)
    (<BooleanPolynomial>self._one_element)._pbpoly = PBBoolePolynomial(1, self._pbring)

    self._monom_monoid = BooleanMonomialMonoid(self)
    self.__interface = {}

    self._names = tuple(char_to_str(_ring.getVariableName(i))
                        for i in range(n))
    self._monom_monoid._names = self._names

    return self


def gauss_on_polys(inp):
    """
    Perform Gaussian elimination on the input list of polynomials.

    INPUT:

    - ``inp`` - an iterable

    EXAMPLES::

        sage: B.<a,b,c,d,e,f> = BooleanPolynomialRing()
        sage: from brial import *
        sage: l = [B.random_element() for _ in range(B.ngens())]
        sage: A,v = Sequence(l,B).coefficient_matrix()
        sage: A
        [1 0 0 0 0 1 0 0 1 1 0 0 0 0 1 0 0 0]
        [0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 1 1 0]
        [0 1 0 1 0 0 1 0 0 0 1 0 0 0 0 0 1 0]
        [0 1 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0]
        [0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 0 0 1]
        [0 1 0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 1]

        sage: e = gauss_on_polys(l)
        sage: E,v = Sequence(e,B).coefficient_matrix()
        sage: E
        [1 0 0 0 0 1 0 0 1 1 0 0 0 0 1 0 0 0]
        [0 1 0 0 0 0 0 0 1 1 1 0 1 1 0 1 0 1]
        [0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 1 1 0]
        [0 0 0 1 0 0 0 1 1 0 0 1 1 1 0 1 1 0]
        [0 0 0 0 1 0 0 1 1 0 1 1 0 1 0 1 0 1]
        [0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 0 0 1]

        sage: A.echelon_form()
        [1 0 0 0 0 1 0 0 1 1 0 0 0 0 1 0 0 0]
        [0 1 0 0 0 0 0 0 1 1 1 0 1 1 0 1 0 1]
        [0 0 1 0 0 0 0 0 0 1 0 0 0 1 0 1 1 0]
        [0 0 0 1 0 0 0 1 1 0 0 1 1 1 0 1 1 0]
        [0 0 0 0 1 0 0 1 1 0 1 1 0 1 0 1 0 1]
        [0 0 0 0 0 0 1 1 0 1 0 1 0 0 0 0 0 1]

    """
    cdef BooleanPolynomialVector _vec = BooleanPolynomialVector(inp)
    return new_BPV_from_PBPolyVector(_vec._parent,
                                     pb_gauss_on_polys(_vec._vec))


def substitute_variables(BooleanPolynomialRing parent, vec, BooleanPolynomial poly):
    """
    ``var(i)`` is replaced by ``vec[i]`` in ``poly``.

    EXAMPLES::

        sage: B.<a,b,c> = BooleanPolynomialRing()
        sage: f = a*b + c + 1
        sage: from brial import substitute_variables
        sage: substitute_variables(B, [a,b,c],f)
        a*b + c + 1
        sage: substitute_variables(B, [a+1,b,c],f)
        a*b + b + c + 1
        sage: substitute_variables(B, [a+1,b+1,c],f)
        a*b + a + b + c
        sage: substitute_variables(B, [a+1,b+1,B(0)],f)
        a*b + a + b

    Substitution is also allowed with different rings::

        sage: B.<a,b,c> = BooleanPolynomialRing()
        sage: f = a*b + c + 1
        sage: B.<w,x,y,z> = BooleanPolynomialRing(order='deglex')

        sage: from brial import substitute_variables
        sage: substitute_variables(B, [x,y,z], f) * w
        w*x*y + w*z + w

    """
    cdef BooleanPolynomialVector _vec

    if isinstance(vec, BooleanPolynomialVector):
        _vec = <BooleanPolynomialVector>vec
    else:
        _vec = BooleanPolynomialVector()
        for f in vec:
            _vec.append(f)
    return new_BP_from_PBPoly(parent, pb_substitute_variables(parent._pbring, _vec._vec, poly._pbpoly))


def set_random_seed(seed):
    """
    The the PolyBoRi random seed to ``seed``

    EXAMPLES::

        sage: from brial import random_set, set_random_seed
        sage: B.<a,b,c,d,e> = BooleanPolynomialRing()
        sage: (a*b*c*d).lm()
        a*b*c*d
        sage: set_random_seed(1337)
        sage: random_set((a*b*c*d).lm(),2)
        {{b}, {c}}
        sage: random_set((a*b*c*d).lm(),2)
        {{a,c,d}, {c}}

        sage: set_random_seed(1337)
        sage: random_set((a*b*c*d).lm(),2)
        {{b}, {c}}
        sage: random_set((a*b*c*d).lm(),2)
        {{a,c,d}, {c}}
    """
    pb_set_random_seed(seed)


def random_set(BooleanMonomial variables, length):
    """
    Return a random set of monomials with ``length`` elements with
    each element in the variables ``variables``.

    EXAMPLES::

        sage: from brial import random_set, set_random_seed
        sage: B.<a,b,c,d,e> = BooleanPolynomialRing()
        sage: (a*b*c*d).lm()
        a*b*c*d
        sage: set_random_seed(1337)
        sage: random_set((a*b*c*d).lm(),10)
        {{a,b,c,d}, {a,b}, {a,c,d}, {a,c}, {b,c,d}, {b,d}, {b}, {c,d}, {c}, {d}}
    """
    cdef PBSet r
    r = pb_random_set(variables._pbmonom, length)
    return new_BS_from_PBSet(r, variables._ring)


def easy_linear_factors(BooleanPolynomial p):
    return new_BPV_from_PBPolyVector(p._parent, pb_easy_linear_factors(p._pbpoly))


# todo: merge with pickling from brial.parallel
def unpickle_BooleanPolynomial(ring, string):
    """
    Unpickle boolean polynomials

    EXAMPLES::

        sage: T = TermOrder('deglex',2)+TermOrder('deglex',2)
        sage: P.<a,b,c,d> = BooleanPolynomialRing(4,order=T)
        sage: loads(dumps(a+b)) == a+b # indirect doctest
        True
    """
    return ring(eval(string,ring.gens_dict()))


# todo: merge with pickling from brial.parallel
def unpickle_BooleanPolynomial0(ring, l):
    """
    Unpickle boolean polynomials

    EXAMPLES::

        sage: T = TermOrder('deglex',2)+TermOrder('deglex',2)
        sage: P.<a,b,c,d> = BooleanPolynomialRing(4,order=T)
        sage: loads(dumps(a+b)) == a+b # indirect doctest
        True
    """
    from brial.parallel import _decode_polynomial
    return _decode_polynomial(l)


# todo: merge with pickling from brial.parallel
def unpickle_BooleanPolynomialRing(n, names, order):
    """
    Unpickle boolean polynomial rings.

    EXAMPLES::

        sage: T = TermOrder('deglex',2)+TermOrder('deglex',2)
        sage: P.<a,b,c,d> = BooleanPolynomialRing(4,order=T)
        sage: loads(dumps(P)) == P  # indirect doctest
        True
    """
    from sage.rings.polynomial.polynomial_ring_constructor import BooleanPolynomialRing_constructor
    return BooleanPolynomialRing_constructor(n, names=names, order=order)


cdef class BooleConstant:
    def __init__(self, int value):
        """
        Construct a boolean constant (modulo 2) from integer value:

        INPUT:

        -  ``i`` - an integer

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: [BooleConstant(i) for i in range(5)]
            [0, 1, 0, 1, 0]
        """
        self._pbconst = PBConstant(value)

    def __repr__(self):
        """
        EXAMPLES::

            sage: from brial import BooleConstant
            sage: repr((BooleConstant(0),BooleConstant(1))) # indirect doctest
            '(0, 1)'

        """
        if self.is_one():
            return '1'
        return '0'

    def deg(self):
        """
        Get degree of boolean constant.

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: BooleConstant(0).deg()
            -1
            sage: BooleConstant(1).deg()
            0
        """
        return self._pbconst.deg()

    def variables(self):
        """
        Get variables (return always and empty tuple).

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: BooleConstant(0).variables()
            ()
            sage: BooleConstant(1).variables()
            ()
        """
        return tuple()

    def is_one(self):
        """
        Check whether boolean constant is one.

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: BooleConstant(0).is_one()
            False
            sage: BooleConstant(1).is_one()
            True
        """
        return self._pbconst.isOne()

    def is_zero(self):
        """
        Check whether boolean constant is zero.

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: BooleConstant(1).is_zero()
            False
            sage: BooleConstant(0).is_zero()
            True
        """
        return self._pbconst.isZero()

    def is_constant(self):
        """
        This is always true for in this case.

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: BooleConstant(1).is_constant()
            True
            sage: BooleConstant(0).is_constant()
            True
        """
        return True

    def has_constant_part(self):
        """
        This is true for `BooleConstant(1)`.

        EXAMPLES::

            sage: from brial import BooleConstant
            sage: BooleConstant(1).has_constant_part()
            True
            sage: BooleConstant(0).has_constant_part()
            False
        """
        return self._pbconst.hasConstantPart()


cdef object pb_block_order(n, order_str,blocks):
    T = [TermOrder(order_str, blockend-blockstart, force=True)
         for (blockstart, blockend) in zip([0] + blocks, blocks + [n])]

    if T:
        result = T[0]
        for elt in T[1:]:
            result += elt
        return result
    else:
        return order_str


cpdef object TermOrder_from_pb_order(int n, order, blocks):
    if not isinstance(order, str):
        if order == pbblock_dlex:
            order_str = pb_block_order(n, "deglex", blocks)
        elif order == pbblock_dp:
            order_str = pb_block_order(n, "degrevlex", blocks)
        elif order == pbblock_dp_asc:
            order_str = pb_block_order(n, "degneglex", blocks)
        else:
            order_str = inv_order_dict[order]
    else:
        order_str = order

    return order_str


cdef class VariableFactory:
    """Implements PolyBoRi's ``Variable()`` constructor and
    a variable factory for given ring """

    def __init__(self, BooleanPolynomialRing ring=None):
        """
        Initialize variable factory, if ring is given.
        Otherwise it initializes a plain constructor

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: fac = VariableFactory()
            sage: fac = VariableFactory(B)

        """
        if ring is not None:
            self._factory = PBVariableFactory(ring._pbring)
        self._ring = ring

    def __call__(self, arg=0, ring=None):
        """
        Return a Variable for ``x``.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: VariableFactory()(B)
            a
            sage: VariableFactory()(0, B)
            a
            sage: VariableFactory(B)()
            a
            sage: VariableFactory(B)(0)
            a

        """
        if ring is None and self._ring is not None:
            return new_BM_from_PBVar(self._ring._monom_monoid, self._ring,
                                     self._factory(<long>arg))
        elif isinstance(arg, BooleanPolynomialRing):
            return arg.variable(0)
        elif isinstance(ring, BooleanPolynomialRing):
            return (<BooleanPolynomialRing>ring).variable(arg)
        else:
            raise TypeError(
                "Cannot convert (%s, %s) to Boolean Variable" %
                (type(arg), type(ring)))


cdef class MonomialFactory:
    """
    Implements PolyBoRi's ``Monomial()`` constructor. If a ring is given is
    can be used as a  Monomial factory for the given ring.


        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: fac = MonomialFactory()
            sage: fac = MonomialFactory(B)

    """
    def __init__(self, BooleanPolynomialRing ring=None):
        """
        Initialized a polynomial factory of ring is given.
        Otherwise it initializes a plain constructor.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: MonomialFactory()(B)
            1
            sage: MonomialFactory()(a.lm())
            a
            sage: MonomialFactory()(a)
            a
            sage: MonomialFactory(B)()
            1
        """
        if ring is not None:
            self._factory = PBMonomialFactory(ring._pbring)
        self._ring = ring

    def __call__(self, arg=None):
        """
        Generates a Boolean monomial from argument.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: MonomialFactory()(B)
            1
            sage: MonomialFactory()(a.lm())
            a
            sage: MonomialFactory()(a)
            a
            sage: MonomialFactory(B)()
            1
        """
        if arg is None and self._ring is not None:
            return new_BM_from_PBMonom(self._ring._monom_monoid, self._ring,
                                       self._factory())
        elif isinstance(arg, BooleanMonomial):
            return arg
        elif isinstance(arg, BooleanPolynomialRing):
            return (<BooleanPolynomialRing>arg)._monom_monoid._one_element
        elif isinstance(arg, BooleanPolynomial) and arg.is_singleton():
            return (<BooleanPolynomial>arg).lm()
        else:
            try:
                result = arg[-1]
                for elt in reversed(arg[:-1]):
                    result = result * elt
                if isinstance(arg, BooleanPolynomial):
                    return result.lm()
                return result
            except Exception:
                raise TypeError(
                    "Cannot %s convert to Boolean Monomial" % type(arg))


cdef class PolynomialFactory:
    """
    Implements PolyBoRi's ``Polynomial()`` constructor and
    a polynomial factory for given rings.
    """
    def __init__(self, BooleanPolynomialRing ring=None):
        """
        Constructs a polynomial factory if ring is given,
        or plain constructor otherwise.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: fac = PolynomialFactory()

        """
        if ring is not None:
            self._factory = PBPolynomialFactory(ring._pbring)
        self._ring = ring

    def lead(self, x):
        """
        Return the leading monomial of boolean polynomial ``x``, with
        respect to the order of parent ring.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: PolynomialFactory().lead(a)
            a
        """
        return x.lead()

    def __call__(self, arg, ring=None):
        """
        Construct a new :class:`BooleanPolynomial` or return ``arg`` if
        it is a :class:`BooleanPolynomial` already.

        EXAMPLES::

            sage: from brial import *
            sage: B.<a,b,c> = BooleanPolynomialRing()
            sage: PolynomialFactory()(1, B)
            1
            sage: PolynomialFactory()(a)
            a
            sage: PolynomialFactory(B)(1)
            1

        """
        if self._ring is None:
            if isinstance(arg, BooleanPolynomial):
                return arg
            elif isinstance(arg, BooleSet):
                return (<BooleSet>arg)._ring._element_constructor_(arg)
            elif isinstance(arg, BooleanMonomial):
                return (<BooleanMonomial>arg)._ring._coerce_(arg)
            elif isinstance(ring, BooleanPolynomialRing):
                return (<BooleanPolynomialRing>ring)._coerce_(arg)
        else:
            if isinstance(arg, int) or isinstance(arg, Integer):
                return new_BP_from_PBPoly(self._ring,
                                          self._factory(<long>arg))

            elif isinstance(arg, BooleanPolynomial):
                return new_BP_from_PBPoly(self._ring,
                                          self._factory((<BooleanPolynomial>arg)._pbpoly))

            elif isinstance(arg, BooleanMonomial):
                return new_BP_from_PBPoly(self._ring,
                                          self._factory((<BooleanMonomial>arg)._pbmonom))

            raise TypeError("Cannot convert %s to BooleanPolynomial" %
                            type(arg))
