元素

可达集合

先行集合

交集

层级

1

1,2,3,4,5,8

1,6,7

1

2

2,3,4,5,8

1,2,3,4,5,6,7,9

2,3,4,5

3

2,3,4,5,8

1,2,3,4,5,6,7,9

2,3,4,5

4

2,3,4,5,8

1,2,3,4,5,6,7,9

2,3,4,5

5

2,3,4,5,8

1,2,3,4,5,6,7,9

2,3,4,5

6

1,2,3,4,5,6,7,8

6

6

7

1,2,3,4,5,7,8

6,7

7

8

8

1,2,3,4,5,6,7,8,9

8

I

9

2,3,4,5,8,9

9

9