\begin{definition}[Definition:Closure/Normed Vector Space]
Let $M = \struct {X, \norm{\, \cdot \,}}$ be a normed vector space.
Let $S \subseteq X$.
The '''closure of $S$ (in $M$)''' is the union of $S$ and $S'$, the set of all limit points of $S$:
:$S^- := S \cup S'$
\end{definition}