This Sudoku puzzle Book presents 500 puzzles to test your solving skills. They are ALL rated HARD (3.0-3.9 per sudokusnake.com rating system - Author not affiliated). At this difficulty level, other basic 'beginner' Sudoku solving techniques are required to solve these puzzles - Techniques that are mostly required for these puzzles -1) Hidden Singles (by Cell/Box), 2) Hidden Singles, 3) Naked Singles, 4) Pointing, and 5) Claiming. The problems are...