ZERO Killer puzzles are played on a standard 9x9 Sudoku frame, but they give you the least amount of starting clues. Unlike ordinary Killer Sudokus, only some cells are grouped in cages, with cage totals shown as usual. Some of the cells are left completely blank. This makes the puzzles even harder than your usual Killer Sudoku. There are 101 of these gems in this book, split into 4 levels of difficulty. The difficulty is only relative to other puzzles in this book. All puzzles are quite difficult and are intended only for the experienced Killer Sudoku aficionado. One puzzle per page is printed, so there is plenty of space to scribble down your notes.