We divide a convex 2009-gon in triangles using non-intersecting diagonals. One of these diagonals is colored green. It is allowed the following operation: for two triangles ABC and BCD from the dividing/separating with a common side BC if the replaced diagonal was green it loses its color and the replacing diagonal becomes green colored. Prove that if we choose any diagonal in advance it can be colored in green after applying the operation described finite number of times. combinatoricsconvex polygonColoringColor problemdiagonal