No one reworks a solved puzzle, making puzzle books perhaps the most disposable of all books. However with its aqueous (water-based) coating and biodegradable soy inks printed on recycled paper, The Green Book of Sudoku 2 wraps 200 challenging and enjoyable Sudoku puzzles in a disposable package that minimizes its effect on our environment. A puzzle can only be solved once, making puzzle books perhaps the most disposable of all books. That's why the Puzzle Society created The Green Book of Sudoku 2. With its aqueous (water-based) coating and biodegradable soy inks printed on recycled paper, this eco-friendly book wraps challenging and enjoyable puzzles in a disposable package that minimizes its effect on our environment. Featuring 200 all-new Sudoku puzzles, The Green Book of Sudoku 2 will keep your brain sharp while you help keep the environment healthy.