Claiming
A digit confined to one box within a line can be removed from the rest of that box.
What it is
Claiming, also called line–box reduction, is the reverse of pointing. If every cell in a row (or column) that could hold a digit lies inside a single box, then that box must supply the digit for the line. The digit is therefore used up within that box, and the box's other cells — those outside the line — can drop it.
How to spot it
Work along rows and columns rather than boxes. For each missing digit, mark the cells on the line that could take it. If they all fall inside one box, apply the elimination to the remaining cells of that box.
Worked example
Step through the reasoning below. Each step adds one layer: first the position, then the pattern, then the candidates involved, and finally what can be eliminated.
Step 1 of 4: The starting position
- Pattern cells
- 5/4, 5/5, 5/6
- Digits
- 5
- Eliminations
- 4/4, 4/5
Press a marked square to point it out on the board above.
Why it matters
Claiming and pointing together handle the interaction between boxes and lines, which is where most of the structure in a Sudoku grid lives. Checking both directions systematically resolves a large share of hard puzzles.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
Is claiming the same as line–box reduction?
Yes, the two names describe the same technique. Some solvers also call it box–line reduction, though that term is ambiguous because it is used for pointing too.
Which should I check first, pointing or claiming?
Pointing tends to be quicker because boxes are compact and easy to scan. Claiming is a good follow-up once the boxes yield nothing.
Put it to use
Where you will meet it
Medium grids are where this move starts to matter: the obvious cells run out and the pattern takes over.
Play MediumStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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