4.1.1.2 Isomorphism Declarations

      ISO-DECL ::= iso-decl SORT+

An isomorphism declaration ISO-DECL is written:

s₁=...=s_n

It declares all the sorts s₁, ..., s_n, as well as their embeddings as subsorts of each other. Thus the carriers for the sorts s_i are required to be isomorphic. The s_i must be distinct.