Proven Sudoku
Techniques / Locked candidates
Locked Candidates Type 2 (Claiming)
Also called Box-Line Reduction, Claiming Pair, Claiming Triple, Type 2 Locked Candidates.
New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.
What it means
Inside one row or column, every spot left for a digit sits in the same box. That box will take the digit from the line, so no other square in the box can be it.
The exact rule, for stronger players
The rule, stated exactly: For a line L and digit d, if every candidate of d within L lies in a single box B, then d may be eliminated from the cells of B outside L.
What it removes: Remove d from all cells of B that are not in L.
Why it works: d must appear somewhere in L. Every available position is in B, so d occupies a cell of B. Since d appears once per box, no other cell of B can hold it.
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
- Locked Candidates Type 1 (Pointing)Inside one box, every spot left for a digit sits in the same row or column.
Related locked candidates
- Locked Candidates (general form)Sometimes all the spots for a digit inside one group also sit inside a second group.
How often does it come up?
Our rough estimate: very common, slightly less so than pointing in most corpora.