Holmes presents the strong collection of very hard sudoku - brain fitness. kakuro levels 17x17, 18x18, 19x19, 20x20. Killer sudoku 8x8 extreme levels. Killer sudoku puzzles with the names: "Sums Sudoku", "Sums Number Place", "Samunamupure", "Kikagaku Nampure", "Sumdoku". Book for superior mental support. Additionally, there are download links for 500 puzzles. I hope you enjoy this book. Best Regards, Basford Holmes