K-th Neighborhood of a vertex

[math]\displaystyle{ k }[/math]-th Neighborhood of a vertex --- окрестность вершины [math]\displaystyle{ k }[/math]-го порядка.

The [math]\displaystyle{ k }[/math]-th neighborhood of a vertex [math]\displaystyle{ v }[/math] of [math]\displaystyle{ G }[/math] is the set of all vertices of distance [math]\displaystyle{ k }[/math] to [math]\displaystyle{ v }[/math], i.e. [math]\displaystyle{ N^{k}(v) = \{u \in V: \; d_{G}(u,v) = k\}. }[/math]