Adjacent arcs

Adjacent arcs --- смежные дуги.

An arc [math]\displaystyle{ (u,v) }[/math] is adjacent to an arc [math]\displaystyle{ (w,z) }[/math] if [math]\displaystyle{ v = w }[/math], and [math]\displaystyle{ (u,v) }[/math] is adjacent from an arc [math]\displaystyle{ (x,y) }[/math] if [math]\displaystyle{ y = u }[/math].