Exercise 1.34.  Suppose we define the procedure

(define (f g)
  (g 2))

Then we have

(f square)
4

(f (lambda (z) (* z (+ z 1))))
6

What happens if we (perversely) ask the interpreter to evaluate the combination 
(f f)? Explain.

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(f f) evaluates to (f 2), which evaluates to (2 2), which is nonsense, as 
2 is not a function.

This is an error which a language with a type system would catch at compile 
time, as f is a function on functions on numbers, so calling f with f as an 
argument can only be an error.