Hard Sudoku puzzle book is a perfect funny Sudoku book for adults. Would you like to improve your logical skills? Love hard Sudoku puzzles? Then you'll love this book! Why play Sudoku? ✓ Sudoku gives your brain the ultimate workout. ✓ It keeps you and your mind healthy and productive. ✓ It helps to maintain and improve your memory. ✓ It also can increase your concentration and focus. 400 enjoyable Hard Sudoku puzzles Hard level: 200 puzzles Extremely Hard level: 200 puzzles Keeps your mind active and performing well. Suitable for all levels: beginner to expert