This question refers to unions and intersections of relations. Since relations are subsets of Cartesian products, their unions and intersections can be calculated as for any subsets. Given two relations R and S from a set A to a set B, R ∪ S = {(x, y) A ✕ B | (x, y) R or (x, y) S} R ∩ S = {(x, y) A ✕ B | (x, y) R and (x, y) S}. Let A = {−2, 2, 7, 9} and B = {2, 7} and define relations R and S from A to B as follows: For every (x, y) A ✕ B, x R y ⇔ |x| = |y| and x S y ⇔ x − y is even.