Definition:Unity (Abstract Algebra)/Ring

Definition
Let $\left({R, +, \circ}\right)$ be a ring.

If the semigroup $\left({R, \circ}\right)$ has an identity, this identity is referred to as the unity of the ring $\left({R, +, \circ}\right)$.

It is (usually) denoted $1_R$, where the subscript denotes the particular ring to which $1_R$ belongs (or often $1$ if there is no danger of ambiguity).

The ring itself is then referred to as a ring with unity.