Normal sudoku rules apply. The grid is partially covered in fog. Entering correct digits will clear the fog from surrounding cells. The number in the top left corner of a red cage (if given) indicates the sum of the digits sandwiched between 1 and 9 in that row. The number in the top left corner of a blue cage (if given) indicates the sum of the digits sandwiched between 1 and 9 in that column. The digit in a cage indicates how many digits (including the crust of 1 and 9) the corresponding sandwich sum contains. “?” can represent any number at all.