Naked Single

Level: Basic

When only one candidate remains in a cell, that number is confirmed.

The Naked Single is the most basic solving technique. If only one candidate number can go in an empty cell, that number is the solution for the cell.

Once you rule out the numbers already placed in the same row, column, and 3×3 box, some cells are left with just one candidate. Turning on notes (pencil marks) makes these cells easy to spot.

It's the first technique to check. After another technique eliminates candidates, rescanning the grid often reveals a chain of new Naked Singles.

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