Normal sudoku rules apply. Some of the grid is covered in fog; entering a correct digit will clear all fog in that digits immediate neighbourhood. Guessing is not required. The 3x3 box borders divide lines into segments, whose sums must strictly increase from one end to the other. No line has more than one segment in any single 3x3 box; different lines are different colours; lines may not branch or share cells with other lines; and lines may cross diagonally but only at cell vertices.