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