Definition:Arborescence/Definition 2

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

That is, let $G$ be an orientation of a tree.

Let $r \in V$.

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


 * For each $v \in V$, $v$ is reachable from $r$.