Let f : A B and g : B C be two functions. As we discussed in class, the composition g f : A C is the function such that for all x A, (g f)(x) = g(f(x)). If g f is onto, does it mean that g must be onto? If so, prove it. If not, provide a counterexample. Hint: Use the formal definition of onto. A function f : X Y is onto if for every y Y , there is an x X such that f(x) = y.