Exercise 1.34

(define (f g) (g 2))

(f square) => 4
(f (lambda (z) (* z (+ z 1)))) => 6

If we try evaluating the combination (f f), we get the process (f f) => (f 2) => (2 2. This fails because 2 is not a procedure:

(f f) =!> "2"