1 2 3 4 =
1 2 3 4 (1 group)
1 | 2 3 4 (2 group)
2 | 1 3 4 (2 group)
3 | 1 2 4 (2 group)
4 | 1 2 3 (2 group)
1 2 | 3 4 (2 group)
1 3 | 2 4 (2 group)
1 4 | 2 3 (2 group)
1 | 2 | 3 4 (3 group)
1 | 3 | 2 4 (3 group)
1 | 4 | 2 3 (3 group)
2 | 3 | 1 4 (3 group)
2 | 4 | 1 3 (3 group)
3 | 4 | 1 2 (3 group)
1 | 2 | 3 | 4 (4 group)