Naked Pair
Two cells in the same unit each have exactly the same two candidates. Those letters must occupy those cells, in some order. Eliminate them from the other cells of that unit.
A letter-based example
Two cells in a row have {A,B} and {A,B}. Remove A and B from every other cell in that row.
A BA B?
Use it on your board
- Choose a row, column or box to inspect. A “unit” means any one of these.
- Check legal candidates against every placed letter. Pencil notes are reminders, not proof: missing or stale notes can hide a possibility.
- Verify every condition in the rule above before making an elimination. A pattern that almost matches is not enough.
- Update the affected notes, then scan for a newly forced letter. A technique often opens the way to a much simpler next move.
Classic and Mega
The candidate rule applies at both board sizes. Classic adds the hidden-line constraint; Mega uses only rows, columns and 5×5 boxes. A larger board has more candidates, so focus on one unit at a time.
These examples explain deductions, not a promise that every generated puzzle requires this technique. In particular, Mega’s launch tiers describe clue density.