Just like in Sudoku, fill in the grid with the digits from 1 to 9. Each group of digits must add up to the number that is just to the left or above it. No group can repeat the same digit twice. Although they are aligned vertically or horizontally, a group does not necessarily span the whole column or row. This means that although you may not repeat a digit within a group, you may repeat it within a column or row. There is no requirement to use all the digits.