Techniques · killer sudoku

Innies & Outies

The 45 rule over two neighbouring rows, columns or boxes leaves one cell whose value is fixed by the cage totals.

In the walkthroughs, every Innies & Outies 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 killer sudoku techniques, or look a puzzle up by number under solutions.