- ➊ Blacken some cells of the diagram [paper] resp. color the
gray cells of the diagram black or white [interactively].
- ➋ A number in a
region indicates how many
cells in this region must be blackened. In a region without a number any number
of cells may be blackened (also none).
- ➌ The black cells must form rectangular
of the region borders.
- ➍ The rectangular areas must not touch