Sudoku techniques · Hard
Naked Pair in Sudoku
A Naked Pair is two cells in the same row, column or box that have shrunk to the same two candidates. Those two numbers have to fill those two cells in some order, so no other cell in the unit can use either of them.
Also known as: Conjugate Pair (cells), Locked Pair.
Why it works
Two cells in the same row, column, or box that have only the same two candidates keep those numbers for themselves.
How to spot it
Look for bivalue cells, meaning cells with exactly two candidates, and then look for a twin.
- The two cells must share a unit and their candidate lists must match exactly. A cell with a third candidate is not part of the pair.
- If the pair also happens to sit in the same box and the same row, it clears both units at once.
- Notes make this nearly free to spot; without notes it is almost invisible.
Builds on
Worked example
These are the app's own lesson boards. Step through them the same way a hint does.
- 1
In this row, each of these two cells has only the candidates 2, 5.
- 2
These two cells together must contain 2, 5, so we can remove the marked candidates from the other cells in this row.
- 3
Done! We've cleaned up the extra candidates and the board is simpler now.