X2 考虑完全图K4的列表边染色 X3 X4 在点V周围，必须满足 X2≠X3)X2-X3≠0 X2≠X5)X2-X5≠0 →(X2-3)(X2-X5)(X3-X5)≠0 X3≠X5)X3-X5≠0 考虑完全图 K4的列表边染色 --------------------------------------------------------- 在点 v 周围，必须满足 x2≠x3  x2-x3≠0 x2≠x5  x2-x5≠0  (x2-x3)(x2-x5)(x3-x5) ≠0 x3≠x5  x3-x5≠0