symmetric difference set: the symmetric difference set of set a and set b is defined as the set of all elements in set a and set b that do not belong to a∩b, recorded as a△b, that is to say, a△b={x|x∈ a∪b,x∉a∩b}, that is, a△b=(a∪b)—(a∩b). that is, a△b=(a—b)∪(b—a)

it is obvious that the symmetric difference set operation satisfies the commutative law: a△b=b△a. the symmetric difference set is also called symmetric difference.