docs: 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