Isomorphic means there exists an 'isomorphism' or an invertible function between two things that aren't the same. So an Array and a List could be Isomorphic, b

Isomorphic means there exists an 'isomorphism' or an invertible function between two things that aren't the same. So an Array and a List could be Isomorphic, but a Set and a List could not be. You could have (I think?) an isomorphism between XML and Javascript (minus CDATA), so it's not relegated to lightly structured types.