Hidden Pair
If two digits can only appear in the same two cells of a unit, those cells can be reduced to just those digits.
Checklist
- Scan candidate positions per digit in one unit.
- Find two digits limited to the same two cells.
- Remove all other candidates from those two cells.
- Rescan linked units for Singles and Pairs.
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 digits limited to two cells
The pair restriction is digit-driven, so those cells can be compressed safely.
Digit-position restriction creates a true hidden pair.
Invalid pattern: one digit appears in three+ cells
Without strict two-cell limitation, Hidden Pair cannot be justified.
Digit spread is too wide for hidden pair logic.
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
Very useful in Medium and often appears before advanced patterns in Hard.
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.