Locked Candidates: Claiming
Box/Line Reduction · Locked Candidates Type 2
In a row (column), digit d lies inside a single box, so d is removed from the other cells of that box.
Rule
Row R has d only inside box B → remove d from box B outside row R.
A digit locked in a row or column
No cell can be filled directly any more. Look at digit 5 in column 8: it can only go in r4c8 and r5c8 — all of them in box 6. Every other empty cell is blocked by the 5 at r2c6 (circled).
The idea
This is pointing in reverse. The row must contain one d; if every possible place for d in the row falls inside the same box, the row's d is in that box.
The box can hold only one d too, and the row has "claimed" it. So no other cell of the box, off that row, can be d.
How to spot it
- Look at rows and columns with few empty cells: if the cells that can still take d all sit in one three-cell segment, try claiming.
- Every box/line intersection can be used in one of two directions: pointing or claiming.
Common mistakes
- Mixing it up with pointing: pointing starts from the box, claiming starts from the row or column.
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Related techniques
References
- HoDoKuLocked Candidates Type 2 (Claiming)(opens in a new tab)
- SudokuWikiIntersection Removal(opens in a new tab)
The examples on this page are generated from random puzzles, not taken from these sources.