Definition:Generator of Subsemigroup

Definition
Let $\left({S, \circ}\right)$ be a semigroup.

Let $\varnothing \subset X \subseteq S$.

Let $\left({T, \circ}\right)$ be the smallest subsemigroup of $\left({S, \circ}\right)$ such that $X \subseteq T$.

Then:
 * $X$ is a generator of $\left({T, \circ}\right)$
 * $X$ generates $\left({T, \circ}\right)$
 * $\left({T, \circ}\right)$ is the subsemigroup of $\left({S, \circ}\right)$ generated by $X$.

This is written $T = \left \langle {X} \right \rangle$.

Also known as
Some sources refer to such an $X$ as a set of generators of $T$, but this terminology is misleading, as it can be interpreted to mean that each of the elements of $X$ is itself a generator of $T$ independently of the other elements.

Also see

 * Definition:Generator


 * Existence of Unique Subsemigroup Generated by Subset