- ➊ Enter a number between 1 and N/2 into each cell of the diagram (N is the size of the region the cell belongs to).
- ➋ Each two cells in a region form a domino. The numbers in the two cells of a domino must be equal.
- ➌ Same numbers must not cover an area of 2x2 cells.
- ➍ A number in a black circle on a border line indicates the sum of the numbers in the adjacent white cells.