Isomorphic Cipher Hierarchy

We can think of the space of ciphers that produce isomorphs as a hierarchy. At the largest level are the ciphers that just produce isomorphs in general. Within this space, there is a region of perfectly isomorphic ciphers. Within this are the group autokey ciphers. Within this are the group ciphertext-autokey ciphers, which can be divided into regions for commutative and non-commutative groups. Within the commutative group-ciphertext autokey region, there is the smallest region in the hierarchy, the (classical) ciphertext-autokey ciphers, corresponding to cyclic groups.

This categorization is very general, and doesn't only apply to the eyes or ciphers like them. For example, ciphers with 83 CT symbols would be a tiny slice out of this entire space, spanning each of the regions (well, sort of, there are no non-commutative group-ciphertext autokey ciphers with 83 CT symbols because 83 is prime, so really there's a section of the CTAK region and a larger section of the GAK region).