Naked Pair
Two cells in a unit with the same two candidates. Those two digits are locked into those cells, so the rest of the unit drops them.
Intermediate sudoku technique
What it is
A naked pair is two empty cells inside a single unit (row, column, or box) whose candidate sets are identical and contain exactly two digits. Since those two digits MUST occupy those two cells in some order, no other cell in that unit can hold either digit. Naked pairs are the first technique to require pencil-mark tracking — you can't reliably spot them without writing candidates in each cell. They're the bedrock of intermediate solving.
When to use it
When the candidate grid is up to date and singles and pointing techniques have stalled. Scan each unit for two cells with the same 2-candidate set.
Worked example
In row 7, cells R7C1 and R7C8 both carry exactly {3, 6} as candidates. Whatever 3 and 6 end up being, one of them is in R7C1 and the other in R7C8. Every other empty cell in row 7 can therefore drop 3 and 6 from its candidates — sometimes that cascade reveals a naked single elsewhere.
Try it
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