Research has shown that a great way to keep your memory and cognitive skills at their best is to learn challenging new things that require you to think. That book offers an accessible way to do just that, since almost everyone knows the basics of solving sudoku, but its variations are nearly endless, and just a small change in the rules can make a big difference in the solving experience. This book features a wide variety of sudoku variants (like Clone Sudoku, Even-Odd Sudoku, Killer Sudoku, and many more), designed to keep solvers on their toes, but presented accessibly, with easier puzzles leading into more complex variations. A freewheeling final chapter combines multiple variations in each puzzle.