Normal sudoku rules apply. The digit in the grey circle is odd. In each set of outside digits, exactly one digit is found in the corresponding row or column in the second box from the clue. All other digits in the set will be found within the first three cells in the row or column from the clue. For instance a '12' clue above column 1 could mean that '1' is found in r123c1 and '2' is found in r456c1, or vice versa.