ref: 47c188c0c6c2a013aded790bcaa5c9640955e38b
dir: /sys/games/lib/sudoku/boards/medium-2005-03-21.su/
..73..8.1 .....73.. 52.1..... ....9...6 962...147 3...2.... .....4.15 ..65..... 4.5..86.. 647352891 189647352 523189764 854791236 962835147 371426589 738264915 296513478 415978623