ref: 52ad5b3ec5138a85e4c976013adbc54642f19b74
dir: /sys/games/lib/sudoku/boards/medium-2005-01-27.su/
1.....7.. 45...8.1. 6.93....5 2.8..1... .6.....8. ...9..5.6 7....53.9 .9.6...51 ..2.....7 123456798 457298613 689317425 278561934 965734182 341982576 716825349 894673251 532149867