Normal sudoku rules apply. Consider the low digits (1, 2, 3), middle digits (4, 5, 6) and high digits (7, 8, 9) as three different groups. Each 2x2 box in the grid has to contain at least one digit of each group.
Normal sudoku rules apply. Consider the low digits (1, 2, 3), middle digits (4, 5, 6) and high digits (7, 8, 9) as three different groups. Each 2x2 box in the grid has to contain at least one digit of each group.