Strongly connected vertices

Strongly connected vertices --- сильно связные вершины.

Two vertices, [math]\displaystyle{ v_{1} }[/math] and [math]\displaystyle{ v_{2} }[/math], are said to be strongly connected, if there is a directed path from [math]\displaystyle{ v_{1} }[/math] to [math]\displaystyle{ v_{2} }[/math] and(!) a directed path from [math]\displaystyle{ v_{2} }[/math] to [math]\displaystyle{ v_{1} }[/math].