(self, sentence)
Remove the sentence's clauses from the KB

        Examples
        ========

        >>> from sympy.logic.inference import PropKB
        >>> from sympy.abc import x, y
        >>> l = PropKB()
        >>> l.clauses
        []

        >>> l.tell(x | y)
        >>> l.clauses
        [Or(x, y)]

        >>> l.retract(x | y)
        >>> l.clauses
        []
Remove the sentence's clauses from the KB
Remove the sentence s clauses from the KB
def retract(self, sentence):
        """Remove the sentence's clauses from the KB

        Examples
        ========

        >>> from sympy.logic.inference import PropKB
        >>> from sympy.abc import x, y
        >>> l = PropKB()
        >>> l.clauses
        []

        >>> l.tell(x | y)
        >>> l.clauses
        [Or(x, y)]

        >>> l.retract(x | y)
        >>> l.clauses
        []
        """
        for c in conjuncts(to_cnf(sentence)):
            if c in self.clauses:
                self.clauses.remove(c)
def retract ( self , sentence ) : for c in conjuncts ( to_cnf ( sentence ) ) : if c in self . clauses : self . clauses . remove ( c )