symmetric difference set (math.)： Collection A and Collection Bsymmetric difference set (math.)define as Collection A and Collection B All those who do not belong to A∩B elemental Collection ，A△B, in other words A△B={x|x∈A∪B,x∉A∩B}，is A△B=(A∪B)—(A∩B).也is B=（A—B）∪（B—A）

It's obvious.，symmetric difference set (math.)calculate (math.) satisfy the commutative law：A△B=B△A，symmetric difference set (math.)也I's called symmetric differential