This is a normal killer sudoku, in which the small digit in the top left of each cage denotes the sum of all the numbers in the cage. Numbers must not be repeated in the cage. However, if there is a 9 in a cage in this sudoku, the 9 is not included in the cage total. For example, if [8 4] is in a cage, the total of the cage is 12, but in a cage with [9 3 4] it is 7.