Hitori

The word "Hitori" actually means "leave me alone!", but these puzzles are sometimes called "the inverse Sudoku", although they are not a Sudoku variety. The book starts with an introduction and a detailed description of solving techniques and examples. In this book there are 150 puzzles in 6 levels of difficulty, ranging in sizes from 5x5 up to a humongous 20x20. Solutions are also included.