Normal sudoku rules apply. Draw a loop, one-cell wide, that moves orthogonally between cells. The loop cannot touch itself, even diagonally: ie If two loop cells are side-by-side, they must be directly connected by the loop; and, if a 2×2 area contains two diagonal loop cells, they must be connected by a third loop cell in that same 2x2. A green circle is on the loop, and its digit indicates the number of cells in its box that are on the loop. A red square is NOT on the loop, and its digit indicates the number of cells in its box that are NOT on the loop. For any two neighbouring cells along the loop, dividing one by the other gives an exact integer (one is a multiple of the other.)