Normal Sudoku rules apply. Digits in two cells separated by an X sum to 10. Digits in two cells separated by a V sum to 5. For any pair of orthogonally adjacent cells where both cells are coloured yellow: The digits cannot add to 5 or 10; the digits cannot be consecutive (ie cannot have a difference of 1); and the digits cannot have a ratio of 1:2 (so one digit cannot be double the other).