Normal sudoku rules apply. Clues outside the grid are either Sandwich, X-Sums or Little Killer, one type each being red, blue and green - grey clues may be any of the types. Sandwich: the sum of the digits between the 1 and the 9 in that row/column is 15; X-Sums: the first X digits from that direction sum to 15, where X is the first digit; Little Killer: 15 is the sum of a diagonal pointing away from the clue, which may include repeats.