I have two types A and B, and I want to express that the composition of two functions f :: B -> A and g :: A -> B gives me the identity idA = f . g :: A -> A. I don't need g . f :: B -> B to be the identity on B, so I want a weaker statement than isomorphism.

I understand that:

(1) If I look at it from the perspective of f, then g is the right inverse or section (or split monomorphism).

(2) If I look at from g, then f is the left inverse or retraction (or split epimorphism).

But I just want two functions that give me an identity on one of the two types and I don't care which function's perspective I'm looking at it from. Is there a word for that?

Regards,

Sean