Claiming (Locked Candidates)
Claiming uses the fact that a digit in one row/column is confined to a single box, allowing eliminations inside that box.
Checklist
- Track one digit in a target row or column.
- Check if all its candidates sit inside one box.
- Eliminate that digit from other cells of the same box.
- Rescan for Singles created by the elimination.
Place in the Learning Course
Treat this page as a lesson, not only a reference. Check the condition, solve one matching puzzle, then review which candidate or cell made the step valid.
1. Find it
Run the checklist in order until you can explain the pattern.
2. Verify it
Compare the valid and invalid diagrams before removing candidates.
3. Practice it
Open the linked difficulty archive and look for the same condition.
Valid pattern: row candidates confined to one box
Because row candidates collapse into one box, other rows in that box cannot keep the same digit.
Confined candidates enabling in-box eliminations.
Invalid pattern: candidates spread across multiple boxes
If the row candidates are not confined, Claiming cannot be applied safely.
Distributed candidates; no Claiming elimination available.
Avoid applying it too early
Use this technique only when every checklist condition is true. A board can look similar while still missing one required limit, and removing a candidate too early can break the puzzle later. Before you act, say which unit, which digit, and which cells make the move valid.
- Fix the row, column, or box you are reasoning about before removing candidates.
- Separate candidates that can be removed from candidates that must remain.
- After the removal, rescan for naked singles or hidden singles created by the update.
How to test it in a real puzzle
After reading the article, do not immediately jump to a harder level. Open one linked difficulty archive and look for the same condition while the checklist is still visible. If the pattern does not appear, that is still useful: write down which row, column, box, digit, or candidate set you checked. That note makes the next related technique easier to choose.
Where to use this
Common in Medium and useful as an opener in Hard puzzles.
Read next
After-Puzzle Review
- Write down one cell or candidate affected by this technique.
- Check whether you almost removed a candidate without the full condition.
- Choose whether to solve one more puzzle at this level or read the related technique first.