Symmetric directed graph

Symmetric directed graph --- симметричный орграф.

This is a digraph [math]\displaystyle{ G = (V,A) }[/math] containing, for every arc [math]\displaystyle{ (v,w) \in A }[/math], the antiparallel arc [math]\displaystyle{ (w,v) \in A }[/math]. A pseudosymmetric digraph is a digraph such that [math]\displaystyle{ deg^{+}(x) = deg^{-}(x) }[/math] at every vertex.