!! +exec+ +vardef+
$lst_tit let$lst_titend$type_exec
  $lst_alias def, define, set
  $(lst_syntax)let $emph name$emphend=$(emph)value$emphend</tt>
  $lst_mean 使变量 $(emph)name$emphend 取值 $(emph)value$emphend. <br/>
  $(emph)value$emphend 可以是变量函数(连同它的可选参数).
