c c petersen graph c has no solution because of sup>2 => one must be green condition c p edge 10 15 e 1 2 e 2 3 e 3 4 e 4 5 e 5 1 e 1 6 e 2 7 e 3 8 e 4 9 e 5 10 e 6 7 e 7 8 e 8 9 e 9 10 e 10 6