Ex-2.5

This is another interesting way to implelment pairs for non-negative integers.

(define (cons a b)
  (* (expt 2 a) (expt 3 b)))
(define (car z)
  (define (iter a count)
    (if (= (remainder a 2) 0)
        (iter (quotient a 2) (+ count 1))
        count))
  (iter z 0))
(define (cdr z)
  (define (iter a count)
    (if (= (remainder a 3) 0)
        (iter (quotient a 3) (+ count 1))
        count))
  (iter z 0))