Now everyone can find the perfect sudoku challenge and become a master at the game. Just like karate, these puzzle collections are ranked by different-colored belts...and they're more precisely and accurately organized by level than ever before. Beginners can start with the extremely easy White Belt (Level 1), and move from book to book as their skills improve. By the time they reach Black (Level 9), they're ready to take on super-tough sudokos. And because the puzzles within each compilation get harder from first to last, too, the final ones are real killers!