def _union(self, other):
        if other.is_FiniteSet:
            return FiniteSet(*(self._elements | other._elements))

        # If other set contains one of my elements, remove it from myself
        if any(sympify(other.contains(x)) is S.true for x in self):
            return set((
                FiniteSet(*[x for x in self
                    if other.contains(x) != True]), other))

        return None
This function should only be used internally
dataset/ETHPy150Open sympy/sympy/sympy/sets/sets.py/FiniteSet._union