- ➊ Blacken some cells of the diagram [paper] resp. color the
gray cells of the diagram black or white [interactively].
- ➋ In each row and each column exactly two cells must be
- ➌ Black cells must not be adjacent, not even diagonally.
- ➍ A number at the edge of the diagram indicates the number of
white cells between the two black cells in the corresponding row or column.