Normal sudoku rules apply. For each line, digits on the line have an equal sum N within each 3x3 box it passes through. If a line passes through the same box more than once, each individual segment of such a line within that box sums to N separately. eg R1c4+r2c4+r3c4+r3c5 = r4c5+r4c6 = r3c6+r3c5+r2c5.