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  "body": "\n## Definition\n\nA directed graph, or digraph, is a pair $D = (V, A)$ of a set $V$ and a relation $A \\subseteq V \\times V$.\nThe elements of $V$ are the vertices of $D$.\nThe elements of $A$ are the arcs, or directed edges, of $D$.\nAn arc $(u, v)$ goes from its tail $u$ to its head $v$.\n\n## Remarks\n\nWith this definition a digraph can have loops $(v, v)$, and it has at most one arc from $u$ to $v$. Some authors exclude loops.\nA [[graph|0JD5C82QMB]] is the same as a digraph whose relation is symmetric and irreflexive.\nThe out-degree of $v$ is the number of arcs with tail $v$, and the in-degree is the number of arcs with head $v$.\n\n## Explanations\n\n### L1 human\n\nA directed graph is a graph whose lines are arrows.\nOne-way streets between crossings form a directed graph.\n",
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