def add_fact(self, *inputs):
        """ Add a fact to the knowledgebase.

        See Also:
            fact
            facts
        """
        fact = tuple(inputs)

        self.facts.add(fact)

        for key in enumerate(inputs):
            if self.index not in key:
                self.index[key] = set()
            self.index[key].add(fact)
dataset/ETHPy150Open logpy/logpy/logpy/facts.py/Relation.add_fact/swapped operands of `not in`