练习2.1

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版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2014/01/14/2014-01-14-练习2.1/

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1.练习2.1

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(define (check-pos-neg a b)
  (or (and (not (< a 0)) (> b 0))
      (and (not (> a 0)) (< b 0))))
(define (make-rat n d)
  (let ((g (gcd (abs n) (abs d)))
	(posi (check-pos-neg n d)))
    (cons (/ (if posi
		 (abs n)
		 (- (abs n)))
	     g)
	  (/ (abs d) g))))
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