1. The problem statement, all variables and given/known data Consider arbitrary sets A, B, C and D with arbitrary functions: f:A-->B, g:B-->C, h:C-->D. We define a composite function h o g o f:A-->D. Given that h, f, and h o g o f are bijective, and g is injective, show that g is also surjective (i.e. g is bijective). This seems almost trivial to me, but my TA says that it requires proving.