Introduced by The Times, the British publisher who pioneered the sudoku craze, the killer sudoku poses a double challenge: the basic rules of sudoku still apply, but puzzles initially have no numbers showing. All that is known is the sum of the numbers inside irregular boxes, called cages, in which the classic 9 x 9 sudoku grid is subdivided. Killer Sudoku contains 101 of these brain-busters grouped into six levels of difficulty. The introduction explains the basic techniques needed to solve these new versions of the world's most popular number puzzle."