Double star

Double star --- двойная звезда.

A double star [math]\displaystyle{ S_{k,k} }[/math] is a tree on [math]\displaystyle{ 2k+2 }[/math] vertices consisting of two adjacent vertices [math]\displaystyle{ u }[/math] and [math]\displaystyle{ v }[/math] of degree [math]\displaystyle{ k+1 }[/math] and 2k end vertices.