Map1 = Map1: unifiable, equal
Map1 = Map1Copy: unifiable, equal
Map1 = Map2: not unifiable, not equal
Map2 = Map1: not unifiable, not equal
Map1 = empty: not unifiable, not equal
empty = Map1: not unifiable, not equal
empty = empty: unifiable, equal
empty = copy(empty): unifiable, equal
Map3 = Map4: not unifiable, equal
Map4 = Map3: not unifiable, equal