(i) If A and B are two nonempty sets, then any subset of the set (A × B) is said to a relation R from set A to set B.

That means, if R be a relation from A to B then R ⊆ (A × B).

Therefore, (x, y) R ⇒ (x, y) (A × B)

That means x is in relation to y. Or we can write xRy.

(ii) Let R be a relation from A to B. Then, the set containing all the first elements of the ordered pairs belonging to R is called Domain.

For the relation R, Dom(R) = {x: (x, y) R}

And the set containing all the second elements of the ordered pair belonging to R is called Range.

For the relation R, Range(R) = {y: (x, y) R}