- ➊ Blacken some cells of the diagram [paper] resp. color the
gray cells of the diagram black or white [interactively].
- ➋ In a row or column of the diagram no number must remain on
a white cell more than once.
- ➌ Black cells must not be
orthogonally adjacent (diagonally
- ➍ All white cells must form a single
orthogonally contiguous area.