It is most natural to think of a binary relation, such as ≤, as taking an ordered pair of elements, such as (3,4) or (6,2), and returning true for the former and false for the latter, as 3 ≤ 4 is true and 6 ≤ 2 is false. More formally, a binary relation on a set S is a subset R of the Cartesian product S × S. We then write aRb if (a,b) ∈ R. See equivalence relation, partial order.