Normal sudoku rules apply. Along 'box-sum lines', digits on the line have the same sum within each 3x3 box the line passes through. The lines must be determined by the solver. All ends of lines are marked with grey dots. Lines can only move orthogonally (ie never diagonally), cannot touch themselves orthogonally, cannot branch and cannot cross themselves or other lines. Lines must start and end in different boxes and cannot re-enter boxes.