Normal sudoku rules apply. Digits in column 1 indicate the column in which the digit 1 appears in that row (e.g. if r4c1 is a 6, r4c6 is a 1). The same applies to columns 5 and 9, with the digits 5 and 9 respectively. Digits along a blue line have an equal sum N within each 3x3 box the line passes through. Different lines may have different values for N.