Draw some straight
lines into the diagram. The sections of the lines run horizontally or vertically
between the center points of
orthogonally adjacent white cells.
- ➋ The lines must pass through all white cells exactly once.
- ➌ A number in a black cell indicates how many lines end on
the four edges of this cell.
- ➍ A number in a white cell indicates the length of the line
passing through this cell.
- ➎ A line must not pass through more than one white number.
- ➏ Not every line must necessarily pass
through a numbered white cell; not every line must necessarily end in a black
cell; a line may connect two black cells.