Rng is a ring whose multiplicative structure doesn't have an identity
(i.e. it is semigroup, not a monoid). Put another way, a Rng is a Ring
without an identity.
Returns a multiplied with itself n times. For instance,
a pow 3 === a * a * a. Since this is a semiring, there is no notion of
a multiplicative identity, and so the exponent must be positive.
Rng is a ring whose multiplicative structure doesn't have an identity (i.e. it is semigroup, not a monoid). Put another way, a Rng is a Ring without an identity.