Overview
- Tier 2
- Intersections
- Typical difficulty
- Peak Score 25–40
- Also known as
- Box-Line Reduction, Locked Candidates Type 2, Claiming Line
When all remaining candidates for a digit in a row or column are confined inside a single 3×3 box, that digit must land in that box, eliminating it from the rest of that box.
Claiming (also called Box-Line Reduction) is the inward mirror of Pointing. The logic flows inward: from the line into the box. If a row or column can only place a digit inside cells that belong to a single 3×3 box, that row/column 'claims' the digit for that box. Consequently, none of the other cells in that 3×3 box can contain that digit.
Worked examples
1 / 5
Reading the exampleCells forming the patternCells losing candidatesEliminated candidates
5
146
49
3479
13467
13469
8
49
2
69
8
7
249
246
469
5
1
3
2
14
3
4589
14
14589
6
49
7
8
46
1
34579
3467
34569
2
67
45
69
7
49
245
1246
1456
3
8
45
3
2
5
478
467
468
1
67
9
7
5
6
34
8
34
9
2
1
1
3
2
6
9
7
4
5
8
4
9
8
1
5
2
7
3
6
In row 2, the digit 4 can only go in R2C4, R2C5 and R2C6, all three in the top-center box. Row 2's 4 must be in that box, so 4 can be removed from the rest of the top-center box.
Removes: 4 from R1C5, R3C5, R1C6, R3C6, R1C4, R3C4
How to apply it
Spotting the pattern and making the deduction, in order.
- Scan a row or column and focus on one candidate digit.
- Check if every remaining candidate for that digit in the line is trapped within the same 3×3 box.
- Because the row or column must contain that digit somewhere, it is guaranteed to land inside that specific box.
- Since that 3×3 box can only contain the digit once, none of the other cells in the box can take it.
- Eliminate that candidate from all other cells in the box that lie outside the original row or column.
Common mistakes
- Scanning only rows and forgetting to check columns.
- Failing to notice an extra candidate hiding in another box along the same row.
- Confusing Claiming with Pointing, leading to incorrect eliminations outside the box.
Frequently asked questions
- Why is it called 'Claiming'?
- Because the row or column 'claims' the digit inside that 3×3 box, preventing any other row or column in that box from claiming it.
- Is Box-Line Reduction the same as Claiming?
- Yes, 'Box-Line Reduction' is the formal mathematical name for Claiming, while 'Pointing' is sometimes called Line-Box Reduction.
- Can Claiming involve three cells?
- Yes, a Claiming Triple occurs when three cells in a row or column all share the same box. The eliminations in the rest of the box are identical.
Related techniques
Put Claiming Pair / Triple into practice
Try a puzzle from the Easy tier (Peak Score 21–30).