Holmes presents the strongest sudoku collection - brain fitness. kakuro levels 7x7, 11x11, 16x16, 20x20. Chain sudoku 9x9 levels easy - very hard. Chain sudoku puzzles with the names: "Sudoku gyrus," "Strimko." Book for superior mental support. Additionally, there are download links for 500 puzzles. I hope you enjoy this book. Best Regards, Basford Holmes