Normal sudoku rules apply. Draw a single non-intersecting loop through the centers of some cells that moves horizontally or vertically and passes through every circle clue. The loop must turn on black circles and pass straight through the cells on either side. The loop must go straight through white circles and turn in at least one of the cells on either side. 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]. The digit in each given circle clue counts the total number of loop cells in all straight loop segments coming off of the cell (counting the cells where the loop turns, and counting the clued cell itself once).