- ➊ Blacken some cells of the diagram [paper] resp. color the gray cells of the diagram black or white [interactively].
- ➋ The black cells divide the diagram in areas of orthogonally contiguous white cells. White areas must not touch each other orthogonally.
- ➌ A cell with a number is always white; for each white area belongs exactly one field with a number. The number in indicates how many fields form the white area.
- ➍ The black cells must form horizontal or vertical stripes, exactly one cell wide. If two stripes are diagonally adjacent, they must be of different length.