Identity
From specialfunctionswiki
Let $X$ be a set. The function $\mathrm{id} \colon X \rightarrow X$ defined by $\mathrm{id}(x)=x$ is called the identity function.
Let $X$ be a set. The function $\mathrm{id} \colon X \rightarrow X$ defined by $\mathrm{id}(x)=x$ is called the identity function.