Antiparallel arcs

Antiparallel arcs --- антипараллельные дуги.

Given a directed graph [math]\displaystyle{ G }[/math], antiparallel arcs are arcs [math]\displaystyle{ (v,w) }[/math] and [math]\displaystyle{ (w,v) }[/math], such that [math]\displaystyle{ v \neq w }[/math].