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