\begin{definition}[Definition:Reachable/Definition 2]
Let $G = \struct {V, A}$ be a directed graph.
Let $\RR$ be the reachability relation of $G$.
That is, $\RR$ is the transitive closure of $A$.
Let $u, v \in V$.
Then $v$ is '''reachable''' from $u$ {{iff}} $u \mathrel \RR v$.
\end{definition}