#| BEGIN (Write your solution here) |#
(define (even? number)
  (= (remainder number 2) 0))

(define (double x) (+ x x))

(define (halve x) (/ x 2))


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

#| END |#