1. The problem statement, all variables and given/known data Can't believe I forgot how to do this... Prove if fog = x and goh = x then f=h for all x. 2. Relevant equations Obviously the associativity of composition here. 3. The attempt at a solution So we know : fog = goh fogoh = gohoh fo(goh) = (goh)oh I've forgotten how to do the rest here.