22. Let F and Fa be fields. A function g E F(F1,F2) is called an even function if g(-t) = g(t) for each t E Fi and is called an odd function if g(-t) = -9(t) for each t E F1. Prove that the set of all even functions in F(F, F) and the set of all odd functions in F(F1, Fa) are subspaces of F(Fi, Fa). A dagger means that this exércise is essential for a later section.