Definition:Arborescence/Definition 2

Definition
Let $G = (V, A)$ be a directed graph.

Let $r \in V$.

Then $G$ is an arborescence of root $r$, an $r$-arborescence, or just an arborescence iff:


 * $(1): \quad$ $G$ is an orientation of a tree.
 * $(2): \quad$ For each $v \in V$, $v$ is reachable from $r$.