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improve chapter 38 readability
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在第二十一章增加一个论文的引用链接
Merge pull request #123 from Klein-Hu/patch-1

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有强迫症的人看到注释没对齐真难受
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Fix some clerical error.
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add all chapter 01's ruby version code based on python's
Merge pull request #126 from RONGHAI/master

add all chapter 01's ruby version code based on python's
change tab to space, and small formatting change
change tab to space
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replace all tabs with spaces
Merge branch 'master' of ssh://github.com/julycoding/The-Art-Of-Programming-By-July
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