SICP 1.20

练习1.20

(define (gcd a b)   (if (= b 0)       a       (gcd b (remainder a b))))

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正则序

(gcd 206 40)(gcd 40 (remainder 206 40))(gcd (rmainder 206 40) (remainder 40 (remainder 206 40)))(gcd (remainder 40 (remainder 206 40)) (remainder (remiander 206 40) (remainder 40 (remainder 206 40))))......

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应用序

(gcd 206 40);(gcd 40 (remainder 206 40))(gcd 40 6);(gcd 6 (remainder 40 6))(gcd 6 4);(gcd 4 (remainder 6 4))(gcd 4 2);(gcd 2 (remainder 4 2))(gcd 2 0)2