Exercise 3.53. Without running the program, describe the elements of the stream defined by
(define s (cons-stream 1 (add-streams s s)))
s是一串2的幂。也就是1、2、4、8、16、32……
【SICP练习】122 练习3.53
原文：http://blog.csdn.net/nomasp/article/details/44707125
