\begin{definition}[Definition:Arborescence/Definition 2]
Let $G = \left({V, A}\right)$ be a directed graph.
Let $r \in V$.
$G$ is an '''arborescence of root $r$''' {{iff}}:
: $(1): \quad$ $G$ is an orientation of a tree
: $(2): \quad$ For each $v \in V$, $v$ is reachable from $r$.
\end{definition}