Normal sudoku rules apply. Outside clues are Sandwich clues, indicating the sum of the cells between the lowest & highest values (usually 1 & 9) seen in their row or column. R0C0 applies this to each of row 0 & column 0 individually. Apart from value 0, every Sandwich clue is unique. (If multiple instances of 0 are seen by R0C0's clue, which is 'lowest' is to be determined by the solver.) Cells across white dots contain consecutive values. Cells across black dots contain one value double the other (1:2 ratio).