Normal sudoku rules apply. Colour each cell either yellow or blue. All cells of the same colour must be orthogonally connected, and no 2x2 area may be all one colour. A purple frame contains two cells of the same colour, and displays the total of the digits of that colour within that 3x3 box (reading left to right, or downwards.) If two digits are joined by an X, they sum to 10. If two digits are joined by a black dot, then one is double the other.