Puzzle: Top1465#2 Toughest Known Puzzle
+-------+-------+-------+
| 7 . 8 | . . . | 3 . . | 
| . . . | 2 . 1 | . . . | 
| 5 . . | . . . | . . . | 
+-------+-------+-------+
| . 4 . | . . . | . 2 6 | 
| 3 . . | . 8 . | . . . | 
| . . . | 1 . . | . 9 . | 
+-------+-------+-------+
| . 9 . | 6 . . | . . 4 | 
| . . . | . 7 . | 5 . . | 
| . . . | . . . | . . . | 
+-------+-------+-------+