(define (mult-rec a b)
  (cond ((= b 0) 0)
	((even? b) (mult-rec (double a) (halve b)))
	(else (+ a (mult-rec a (- b 1))))))

(define (mult-iter a b n)
  (cond ((= b 0) n)
	((even? b) (mult-iter (double a) (halve b) n))
	(else (mult-iter a (- b 1) (+ a n)))))

(define (mult a b)
  (mult-iter a b 0))

(define (double a) (+ a a))

(define (halve a) (/ a 2))