We have functions $f: E \rightarrow F$ and $g: F \rightarrow G$.
Suppose that $ g \circ f $ and $g$ are bijective, show that $f$ is bijective.
In the previous exercises, I have proven that if $ g \circ f $ is injective then $ f$ is injective and that if $ g \circ f $ is surjective, then $g$ is surjective.
However, I am stuck on this one, as I only have to prove that $f$ is surjective. If the solution is trivial, hints would be fine.