Definition:Endomorphism Ring of Abelian Group

Definition
Let $(G,+)$ be an abelian group.

Let $\operatorname{End}(G)$ be the set of endomorphisms of $G$.

Then $(\operatorname{End}(G),+,\circ)$ is called the endomorphism ring of $G$

where $\circ$ denotes composition and $+$ denotes pointwise addition.

in Endomorphism Ring of Abelian Group is Ring, it is shown that $(\operatorname{End}(G),+,\circ)$ is a ring.