Topological Closure is Closed

Theorem
Let $T$ be a topological space.

Let $H \subseteq T$.

Then $\operatorname{cl}\left({H}\right)$ is closed.

Proof
From Closure of Closure equals Closure, we have that $\operatorname{cl}\left({\operatorname{cl}\left({H}\right)}\right) = \operatorname{cl}\left({H}\right)$.

From Closed Set Equals its Closure, it follows that $\operatorname{cl}\left({H}\right)$ is closed.