ref: 6972974f8df3ead3043185c046b7871110b85b79
dir: /sys/games/lib/sudoku/boards/medium-2005-02-15.su/
.6.531..7 .7....8.5 .....74.. 2...63... .5.....2. ...42...6 ..21..... 4.8....5. 5..849.3. 864531297 173294865 925687413 241763589 657918324 389425176 732156948 498372651 516849732