+---+---+---+---+---+---+
| x | 1 | 2 | 3 | 4 | 5 |
+---+---+---+---+---+---+
| B | x | x | x |   |   |
| 1 | x | x | x | x | x |
| 2 | x | x | x | x | x |
| 3 | x | x | x | x | x |
| 4 | x | x | x |   |   |
| 5 |   |   |   |   |   |
| 6 |   |   |   |   |   |
+---+---+---+---+---+---+