\begin{definition}[Definition:Multigraph]
A '''multigraph''' is a graph that can have more than one edge between a pair of vertices.
That is, $G = \struct {V, E}$ is a '''multigraph''' if $V$ is a set and $E$ is a multiset of doubleton subsets of $V$.
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The graph above is a '''multigraph''' because of the double edge between $B$ and $C$ and the triple edge between $E$ and $F$.
\end{definition}