Find the relation described: |x| = y. (Remember that absolute value thing from way back when?)
Answer
x and y can be any real numbers, so this is one of those massive, ridiculous relations:
{(1, 1), (-1, 1), (2, 2), (-2, 2), (3, 3), (-3, 3), . . . ,
(e, e), (-e, e), (π, π), (-π, π), . . . }