Details can be found here.
Type-equivalence is an asymmetric relation which holds between two types, A and B.
A is type-equivalent to B iff
- the identity of A is equal to the identity of B, OR
- the identity of B is Z1, OR
- the keys in A stand in a 1:1 relationship to the keys in B, and the type of every key in A is type-equivalent to the type of the corresponding key in B