From Wikipedia article "Sudoku": . . . | 1 . . | 7 4 . . 5 . | . 9 . | . 3 2 . . 6 | 7 . . | 9 . . ------+-------+------ 4 . . | 8 . . | . . . . 2 . | . . . | . 1 . . . . | . . 9 | . . 5 ------+-------+------ . . 4 | . . 7 | 3 . . 7 3 . | . 2 . | . 6 . . 6 5 | . . 4 | . . . http://en.wikipedia.org/wiki/Sudoku