In

set theory, the symmetric

difference of two

sets A and B is the set of elements which appear in exactly one of A or B. In other words, it is the

union of A and B

minus their

intersection. This operator is both

commutative and

associative. It is usually represented by an uppercase

delta.

For example, consider the set of positive even numbers, and the set of positive multiples of 3. The symmetric difference of these two sets is the set {2, 3, 4, 8, 9, 10, 14, 15, 16, ...}