Definition 2.2 A semiring (S,+, ·) is said to be additively commutative if
(S, +) is a commutative semi group. A semiring (S,+, ·) is said to be multiplicatively
commutative if (S, ·) is a commutative semi group. It is said to be
commutative if both (S, +) and (S, ·) are commutative.