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Killer Sudoku VariantsOne puzzle is called killer sudoku pro, and this includes all the usual killer sudoku rules but with exception  not just addition is used, but other mathematical operations too. For instance subtraction, division and multiplication. Typically when these puzzles appear they disallow any noninteger answers, so that puts a restriction on the division possible, and they also restrict any zero or negative totals, which restricts the possible combinations for the subtraction regions too. Whilst having multiplication as well as addition is straightforward, because the order matters with division and subtraction a new rule is applied in those cases. This rule says that you start with the highest number in any given cage and then divide or subtract the other smaller numbers from that one number. There are other variants of killer sudoku too. These variants are all great if you love the challenge of games, but are hoping to try something a little more mathematically complex. One of the most popular is called kenken, also known as calcudoku, kendoku and a range of other names too. This puzzle has no box regions at all, and therefore is more about the maths than sudoku to some extent. Also it has thick border lines rather than dotted cages as there are no bold regions. There is another difference with this puzzle and killer sudoku, in that for the first time repetition IS allowed within the sum regions, just so long as that repetition does not conflict with the rule that each number appears once in each row and column. This can be very confusing the first few puzzles that you play, as by doing sudoku, kakuro and killer sudoku over the years many have grown up with logic puzzles that always prohibit repetition. However, when you get used to it it can be quite interesting as of course it introduces more possible combinations for many regions. There are probably other variants of killer sudoku too, but these are the main ones. Just occasionally you will see regions without a total or without display the operation that is performed, and in those cases you must use the information in the rest of the puzzle to find what the answers are. 