Claiming Pair & Triple — Box-Line Reduction
The mirror of pointing pair. A digit restricted to one box within a row or column gets eliminated from the rest of that box.
Intermediate sudoku technique
What it is
A claiming pair or claiming triple is the row/column-to-box version of the pointing technique. Pick a row or column, look at where a digit could go inside it. If every viable cell lies within a single 3×3 box, the digit MUST land in that box from this row's perspective — and therefore cannot appear elsewhere in that box. Claiming techniques (also called box-line reduction) and pointing techniques work together: pointing flows box → line, claiming flows line → box. Both prune candidates without placing.
When to use it
After singles and pointing techniques dry up. Walk each row and each column digit by digit; whenever a digit collapses to a single box, run the claiming elimination on that box.
Worked example
In row 4, the digit 8 can only go in R4C4, R4C5, or R4C6 — all three cells live in box 5 (the centre 3×3). So 8 must be placed somewhere in box 5 from row 4's perspective. Therefore 8 cannot appear in row 5 or row 6 of box 5: R5C4, R5C5, R5C6, R6C4, R6C5, R6C6 all lose 8 as a candidate.
Try it
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