1 (defun double (x)
2   (* x 2))
3 (defun halve (x)
4   (/ x 2))
5 (defun fast-mult (a b)
6   (cond ((= b 0) 0)
7 	((= b 1) a)
8 	((evenp b) (double (fast-mult a (halve b))))
9 	(t (+ a (fast-mult a (- b 1))))))