Puzzle: TopN87#57 2-constrained
+-------+-------+-------+
| 7 . . | . . . | 4 . . | 
| . 2 . | . 7 . | . 8 . | 
| . . 3 | . . 8 | . . 9 | 
+-------+-------+-------+
| . . . | 5 . . | 3 . . | 
| . 6 . | . 2 . | . 9 . | 
| . . 1 | . . 7 | . . 6 | 
+-------+-------+-------+
| . . . | 3 . . | 9 . . | 
| . 3 . | . 4 . | . 6 . | 
| . . 9 | . . 1 | . . 5 | 
+-------+-------+-------+