Fib数的算法

(define (fib-iter a b p q count)
  (cond ((= count 0) b)
        ((even? count)
         (fib-iter a b
                   (+ (square p) (square q))
                   (+ (square q) (* 2 p q))
                   (/ count 2)))
        (else (fib-iter
               (+ (* b q) (* a q) (* a p))
               (+ (* b p) (* a q))
               p
               q
               (- count 1)))
        )
  )
        

(define (fib n)
  (fib-iter 1 0 0 1 n)
  )