Disc

Disc --- диск, окрестность порядка [math]\displaystyle{ k }[/math].

Let [math]\displaystyle{ v }[/math] be a vertex of [math]\displaystyle{ G }[/math]. A disc centered at [math]\displaystyle{ v }[/math] with a radius [math]\displaystyle{ k }[/math] is the set of all vertices whose distance to [math]\displaystyle{ v }[/math] is at most [math]\displaystyle{ k }[/math] : [math]\displaystyle{ N^{k}[v] = \{u: \; u \in V\mbox{ and }d(u,v) \leq k\} }[/math].