The Big Book of Logic Puzzles - Kakuro 400 Hard (Volume 5)

Kakuro (also known as "Cross Sums", "Kakro") is a logic puzzle, a mathematical equivalent of crosswords. The puzzle consists of a playing area of filled and empty cells similar to a crossword puzzle. Some black cells contain a diagonal slash from top left to bottom right with numbers in them, called "the clues". A number in the top right corner relates to an "across" clue and one in the bottom left a "down" clue. The object of a kakuro is to insert digits from 1 to 9 into the white cells to total the clue associated with it. However no digit can be duplicated in an entry. For example the total 6 you could have 1 and 5, 2 and 4 but not 3 and 3.