Techniques · sudoku and killer sudoku

Box-Line Reduction

Inside a row or column, a digit is confined to one box. It must go in that line, so it can be removed from the rest of the box.

In the walkthroughs, every Box-Line Reduction step shades the cells of the pattern and names the cell and digit it proves, so you can see the move on the grid rather than read about it. Press “Skip to next hard step” to jump straight to it.

None of the walkthroughs published so far needs this one; it is here for completeness.

Where it sits

See the whole ladder on hard sudoku techniques and hard killer sudoku techniques, or look a puzzle up by number under solutions.