Normal sudoku rules apply. The grid is mostly covered in fog; placing a correct digit removes fog in surrounding cells. No guessing is required. A red "X" indicates a product square: a 2x2 region of cells where the product of the digits on the negative diagonal equals the product of the digits on the positive diagonal. A blue "X" indicates a sum square: a 2x2 region of cells where the sum of the digits on the negative diagonal equals the sum of the digits on the positive diagonal. Digits in cells separated by a white dot must be consecutive. No rule is subject to a negative constraint.