Normal sudoku rules apply. Digits do not repeat along a marked blue diagonal. A diamond shows that there exist two digits N steps away from the diamond in an orthogonal direction that have a difference of N, where N is the digit in the diamond. Not all diamonds are necessarily given. (For example, if r6c4 is a 3, then at least one pair of digits from the set of digits in r3c4, r6c7, r9c4 and r6c1 must have a difference of 3).