+ if isinstance(other, Domain):
+ symbols = self._xsymbols([self, other])
+ islset1 = self._toislset(self.polyhedra, symbols)
+ islset2 = other._toislset(other.polyhedra, symbols)
+ islset = libisl.isl_set_union(islset1, islset2)
+ return self._fromislset(islset, symbols)
+ return NotImplemented