Warning 1.1.6.2. The terminology of Definition 1.1.6.1 is not standard. Note that a directed graph $G$ can have distinct edges $e \neq e'$ having the same source $s(e) = s(e')$ and target $t(e) = t(e')$ (for this reason, directed graphs in the sense of Definition 1.1.6.1 are sometimes called multigraphs). Definition 1.1.6.1 also allows graphs which contain loops: that is, edges $e$ satisfying $s(e) = t(e)$.
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$