\begin{definition}[Definition:Directed Graph/Symmetric Digraph]
Let $D = \struct {V, E}$ be a digraph such that the relation $E$ in $D$ is symmetric.
Then $D$ is called a '''symmetric digraph'''.
It follows from the definition of a (simple) graph that a '''symmetric digraph''' is in fact the same thing as an undirected graph.
\end{definition}