1. About permuter index.
url: https://www.youtube.com/watch?v=j789k96g5aQ&list=PL0ZVw5-GryEkGAQT7lX7oIHqyDPeUyOMQ&index=28
FAQ and discussed with adam
原文：https://www.cnblogs.com/yyagrt/p/11516790.html
