Normal sudoku rules apply. Cells separated by a white dot contain consecutive digits. Cells separated by a black dot contain digits with a 2:1 ratio (ie one digit will be double the other). Not all possible dots are necessarily given. Digits in a circle must appear in at least one of the four surrounding cells. Draw a one-cell-wide loop of orthogonally connected cells. The loop may not touch itself, not even diagonally. The loop must enter exactly one of the four cells surrounding each given quad clue. The loop acts as a modular line. Each set of three adjacent digits along the loop must be one each from the sets [147], [258], and [369].