!! +exec+ +vardef+
$lst_tit exchange$lst_titend$type_exec
  $(lst_syntax)exchange$emph var1$emphend and
  $emph var2$emphend</tt> <br/>
  或 <tt>exchange$emph var1$emphend, $emph var2$emphend</tt>
  $lst_mean 交换变量 $emph var1$emphend 与 $emph var2$emphend 的值.
  
