\begin{definition}[Definition:Closure (Topology)/Definition 4]
Let $T = \struct {S, \tau}$ be a topological space.
Let $H \subseteq S$.
The '''closure of $H$ (in $T$)''' is defined as the union of $H$ and its boundary in $T$:
:$H^- := H \cup \partial H$
\end{definition}