作者：未知 来源：月光软件站 加入时间：2005-5-13　月光软件站

; ======================================================================
;
;          Structure and Interpretation of Computer Programs
;                  (trial answer to excercises)
;
;                  计算机程序的构造和解释(习题试解)
;
;                                             created: code17 04/25/05
;                                             modified:
; (保持内容完整不变前提下，可以任意转载)
; ======================================================================


;; SICP No.2.10

(define (div-interval x y)
  (let ((y-l (lower-bound y))
        (y-u (upper-bound y)))
    (if (< (* y-l y-u) 0)
      (error "divisor interval expands zero")
      (mul-interval x
                    (make-interval 
                     (/ 1.0 y-u)
                     (/ 1.0 y-l))))))


;; Test-it:
;; Welcome to MzScheme version 209, Copyright (c) 2004 PLT Scheme, Inc.
;; ;; .............
;; > test1
;; (3 . 5)
;; > test3
;; (-5 . 3)
;; > (div-interval test1 test3)
;; divisor interval expands zero
;; > (div-interval test3 test1)
;; (-1.6666666666666665 . 1.0)

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