Binary Relation

First element comes from a set called the domain.

Second element comes from a set called the codomain.

D1 = {a, b, c}

C1 = {0, 1}

B1 = {(a, 0), (a, 1), (c, 0), (c, 1)}

B1 is a binary with domain D1 and codomain C1.

Often, however, the domain and codomain are identical.

D2 = C2 = {a, b, c}

B2 = { (a, a), (b, b), (c, c), (a, c), (c, a)}

B2 is a binary relation on D2.