- ➊ Place exactly one arrow into each
region of the diagram, oriented either horizontally or vertically.
- ➋ Each two arrows are paired, i.e. they point to each other;
there are no unpaired arrows.
- ➌ Between two paired arrows at least one region must exist in
which none of the two paired arrows is placed.
- ➍ Between two paired arrows no other arrow must be placed.