1.
参考链接:
a. http://article.yeeyan.org/view/6774/2620
b. http://www.zhihu.com/question/20161362
c. http://www.360doc.com/content/12/0610/14/10160908_217229878.shtml
d. http://www.ha97.com/4105.html
e. http://blog.sciencenet.cn/blog-734884-667157.html