(define (fast-expt x n)
  (if (even? n)
      (expt (expt x (/ n 2)) 2)
      (expt x n)))

(define (expt x n)
  (cond ((= n 0) 1)
        ((= n 1) x)
        ((= n -1) (/ 1 x))
        ((< n 0) (* (/ 1 x) (expt x (+ n 1))))
        (else (* x (expt x (- n 1)))))