(define (exponent a n)(cond((= n 0)1)
                             (else(* a (exponent a (- n 1))))))

(define (exponent-iter b a n)(cond ((= n 0) b)
                                     (else(exponent-iter (* b a) a (- n 1)))))

(define (fast-exponent a n)(cond((= 0 n)1)
                                  ((even? n)(square (fast-exponent a (/ n 2))))
                                  (else(* a (fast-exponent a (- n 1))))))