C#取两个集合的交集、并集和差集

用到三个API：

交集：Intersect

并集：Union

差集：Except

var A=new List(){1,2,3,4,5,6};
var B=new List(){3,4,5,6,7,8,9};
var C=A.Intersect(B);//交集{3,4,5,6}
var D=A.Union(B);//并集{1,2,3,4,5,6,7,8,9}
var E=A.Except(B);//差集{1,2}
var F=B.Except(A);//差集{7,8,9}