Sum-thing big is on the horizon Kakuro puzzles (also known as cross sums) are like a combination of crosswords and sudoku: each clue in the grid tells you the sum of the digits in its answer, and just like sudoku, digits are never repeated within an answer.From this simple premise, extremely challenging puzzles can be constructed, and that’s just what Conceptis Puzzles has done for these collections, which each contain 72 supersized kakuro, offering massive solving pleasure for the brave souls who love tackling such challenges.