What does it mean for a set to contradict another? If a merge results
        in the empty set -- when both sets are disjoint.

        CONTRADICTION: self = {4} other = {3}
        NOT CONTRADICTION: self = {4} other = {3,4}
        NOT CONTRADICTION: self = {3,4} other = {3}

def is_contradictory(self, other):
        """
        What does it mean for a set to contradict another? If a merge results
        in the empty set -- when both sets are disjoint.

        CONTRADICTION: self = {4} other = {3}
        NOT CONTRADICTION: self = {4} other = {3,4}
        NOT CONTRADICTION: self = {3,4} other = {3}
        """
        other = self.coerce(other)
        # contradictory if both values are disjoint
        return self.get_values().isdisjoint(other.get_values())