第二章习题 2.1 - 2.32 的解答。
E-2.1:
(define (numer x) (car x))
(define (denom x) (cdr x))
(define (print-rat x)
(display (numer x))
(display "/")
(display (denom x))
(newline))
; -------------------------------------------
(define (make-rat n d)
(if (or (and (> n 0)
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