List之Union(),Intersect(),Except()

http://www.cnblogs.com/qinpengming/archive/2012/12/03/2800202.html List之Union(),Intersect(),Except() 亦可以说是数学中的并集，交集，差集

http://blog.csdn.net/lingxyd_0/article/details/20877721  C# 对List<T>取交集、连集及差集

https://msdn.microsoft.com/en-us/library/bb336390.aspx

https://msdn.microsoft.com/en-us/library/bb300779(v=vs.100).aspx