Sudoku Fusion puzzles play the same as Killer Sudoku, the Sudoku variation that is wildly popular. Pocket Posh Sudoku Fusion presents 100 puzzles in four difficulty levels. In addition to the rules of traditional Sudoku, the sum of the digits in each inner cage must equal the number in the top left corner of the cage. This portable package is part of a best-selling series featuring highly stylized, embellished covers and boasting 5 million copies in print. A free trial subscription to The Puzzle Society(TM) adds extra value.