## Alpha Now, Omega Later : 5

• “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 $L$ is a triadic relation of the form $L \subseteq O \times S \times I,$ where $O$ is a set of formal objects under consideration and $S$ and $I$ are two formal languages used to denote those objects.  It is common practice to cut one’s teeth on the special case $S = I$ 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.