- Blacken some cells of the grid [on paper] or color the
gray cells of the grid either black or white [interactively].
- The black cells divide the grid in islands, areas of
orthogonally-connected white cells.
- The islands must not touch each other
orthogonally.
- All cells with a number belong to an islands; to an island belongs exactly
one cell with a number. The number indicates how many cells belong to the
island.
- No area of 2x2 fields may be completely black.
- All black cells must form a single
orthogonally-connected area.
Additional Rules:
Each white region contains exactla two numbers. The size of the
region must be strictly between these two numbers.