\begin{definition}[Definition:Closed Disk]
Let $V$ be a vectorspace and $x \in V$, $r \in \R$. Then the '''closed disk''' $\bar{D}$ centered at $x$ with radius $r$ is the set:
{{begin-eqn}}
$\bar{D}(x, r) := \{v \in V | \| x - v \| \le r\}$
{{end-eqn}}
\end{definition}