Remark 1.1.6.3. It will sometimes be convenient to represent a directed graph $G$ by a diagram, having a node for each vertex $v$ of $G$ and an arrow for each edge $e$ of $G$, directed from the source of $e$ to the target of $e$. For example, the diagram

\[ \xymatrix@R =50pt@C=50pt{ & \bullet \ar@ /^2pc/[dr] \ar [dr] & \\ \bullet \ar@ /^1.5pc/[rr] \ar [ur] & & \bullet \ar [ll] } \]

represents a directed graph with three vertices and five edges.