The substobj type exposed to clients in https://github.com/anoma/geb/blob/main/src/specs/geb.lisp should be extended to include another binary constructor, called something like hom, which constructs the hom-object (the type of morphisms) from its first parameter to its second. (Currently, clients have to compute the hom-object themselves; they should not be subjected to this.)

Geb can straightforwardly compute the hom-object in its Lisp implementation as the types currently stand; it might take a bit of thought to integrate with the upcoming built-in natural number types (i.e. arithmetic mod n for each natural number n-- see #61 ).

VampIR higher-order functions might be helpful in integrating this with #61 ; see https://github.com/anoma/vamp-ir/blob/main/tests/funcs.pir for examples.