\begin{definition}[Definition:Directed Graph/Arc]
Let $G = \struct {V, E}$ be a digraph.
The '''arcs''' are the elements of $E$.
Informally, an '''arc''' is a line that joins one vertex to another.
If $e \in E$ is an '''arc''' joining the vertex $u$ to the vertex $v$, it is denoted $u v$.
\end{definition}