Proven Sudoku
Locked Pair
Also called Locked Naked Pair, Intersection Pair.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
A pair that shares two groups at once, usually a row and a box. Because it sits in both, you can rub the two digits out of both groups, not just one.
The exact rule, for stronger players
The rule, stated exactly: A Naked Pair whose two cells share two houses, that is, both lie in the same box and the same line. The elimination applies in both houses.
What it removes: Remove both digits from all other cells of the box and of the line.
Why it works: The naked pair argument holds independently in each house the pair occupies. Sharing two houses simply means the same pair licenses eliminations in both.
Worked examples
These come from real Proven Sudoku boards. Nobody drew them by hand to make the pattern look neat. Each one is checked first, so the board is one you could really meet, the pattern is really there, and every digit it rules out is really wrong.
Learn these first
- Naked PairTwo squares in the same group both hold only the same two digits.
Related subsets
- Locked TripleA triple that sits in two groups at once, usually a row and a box.
- Naked QuadFour squares in one group share the same four digits between them.
- Naked Subset (general form)Find some squares in one row, column or box.
- Naked TripleThree squares in one group share the same three digits between them.
- Hidden PairTwo digits in one group can only go in the same two squares.
How often does it come up?
Our rough estimate: common wherever naked pairs occur inside a single box.