5. Here are three important combinators, which are lambda terms with no free variables: I-Xx.x (it is called the identity function) It can be shown that any combinators can be generated from S and K using only function application. (a) Show that the expression S K K reduces to the identity function I (b) Show the result of applying -reduction to the expression (S (K S) K) x y z until no more beta reductions can be applied