Coalescing of two rooted graphs

Coalescing of two rooted graphs --- срастание двух корневых графов.

A coalescing of two rooted graphs [math]\displaystyle{ (G,u) }[/math] and [math]\displaystyle{ (H,v) }[/math], denoted [math]\displaystyle{ G.H }[/math], is defined by Schwenk as a graph obtained by identifying the two roots so that [math]\displaystyle{ u=v }[/math] becomes a cut-vertex of [math]\displaystyle{ G.H }[/math].