Re: R.J. Lipton and K.W. Regan • Isomorphism Is Where It’s At

• “Are there more good cases of isomorphism to study?”

Just off the top of my head, a couple of examples come to mind.

Sign Relations.  In computational settings, a sign relation is a triadic relation of the form where is a set of formal objects under consideration and and are two formal languages used to denote those objects.  It is common practice to cut one’s teeth on the special case before moving on to more solid diets.

Cactus Graphs.  In particular, a variant of cactus graphs known (by me, anyway) as painted and rooted cacti (PARCs) affords us with a very efficient graphical syntax for propositional calculus.

I’ll post a few links in the next couple of comments.