- ➊ Blacken some
regions of the diagram [paper] resp. color the gray regions of the diagram
black or white [interactively].
- ➋ A number in a cell indicates the number of black cells in
orthogonally adjacent cells.
- ➌ There are no areas of size 2×2 cells which are completely
black or white.
- ➍ All black cells must form a single
orthogonally contiguous area.