2,4,5,6} 2,36} 2 {1,3,5,6}是否割集? 52 4 5 6 {2,4,5,6} 1 3 2 {2,3,6} 1 4 5 • 1 2 3 4 6 5 7 {1,3,5,6}是否割集？ 2 4 7 1 3