+---------+---------+---------+
| .  .  . | .  .  8 | .  1  . |
| .  3  7 | .  .  . | .  .  . |
| .  5  . | .  7  . | 4  .  9 |
+---------+---------+---------+
| .  .  . | .  .  . | 2  .  . |
| .  .  . | 6  .  . | .  .  . |
| 4  1  . | .  .  2 | .  .  3 |
+---------+---------+---------+
| .  7  1 | .  .  . | .  .  . |
| .  .  9 | .  2  . | 6  .  4 |
| .  .  6 | .  9  3 | 5  .  . |
+---------+---------+---------+
