Naked Pair
When two cells in one unit share the exact same two candidates, those candidates are locked to those cells.
Checklist
- Find two candidate cells inside one unit.
- Confirm both candidate sets are exactly identical.
- Eliminate those two digits from other cells in the unit.
- Check for newly created Singles.
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: two cells locked to the same pair
A shared pair (for example {2,7}) allows direct eliminations from all other cells in the unit.
Locked pair enabling unit-wide elimination.
Invalid pattern: one cell has extra candidate
If one cell has a third candidate, the pair is not locked and elimination is unsafe.
Unstable pair with extra candidate.
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
Frequent in late Easy and throughout Medium.
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.