Proper (vertex) colouring

Proper (vertex) colouring --- правильная раскраска (вершин).

A proper colouring of [math]\displaystyle{ G }[/math] is an assignment of colors to the vertices so that adjacent vertices obtain distinct colors. The chromatic number [math]\displaystyle{ \chi(G) }[/math] is the minimum number of colors required among all proper colorings of [math]\displaystyle{ G }[/math].