Radius-essential edge

Radius-essential edge --- радиус-существенное ребро.

An edge [math]\displaystyle{ e }[/math] is radius-essential if [math]\displaystyle{ rad(G/e) \lt rad(G) }[/math]. The number of radius-essential edges in a graph [math]\displaystyle{ G }[/math] is denoted by [math]\displaystyle{ c_{r}(G) }[/math].