def not_(self, *query_expressions):
        ''' Add a $not expression to the query, negating the query expressions
            given.

            **Examples**: ``query.not_(SomeDocClass.age <= 18)`` becomes ``{'age' : { '$not' : { '$gt' : 18 } }}``

            :param query_expressions: Instances of :class:`ommongo.query_expression.QueryExpression`
            '''
        for qe in query_expressions:
            self.filter(qe.not_())
        return self