Naked single or hidden single? The beginner-friendly difference
Both methods prove one placement. The difference is where you look: either inspect the candidates inside one cell, or follow one digit across a row, column, or 3×3 box.
Definition
A naked single leaves one candidate in a cell. A hidden single leaves one possible cell for a digit in a row, column, or 3×3 box.
A placement can be forced because one cell has one candidate, or because one digit has one possible cell in a row, column, or 3×3 box.
- First check: inspect one cellIf one cell contains just one candidate, that digit must go there. This is called a naked single.
- Second check: follow one digitR4C6 still contains candidates 6 and 7, so the cell itself is not solved. But none of the other eight cells in row 4 contains candidate 7.
- Place 7 in its only possible cellPlace 7 in R4C6. Because 7 was hidden among another candidate in its cell, this is called a hidden single.
R4C6 is not a naked single: it still contains candidates 6 and 7. But it is the only cell in row 4 that contains candidate 7, so 7 must go there. That is the hidden-single proof.
A reference verified by Doku.su
Doku.su checks every placement or elimination in this example with its deterministic Sudoku engine. Illustrative candidates are labelled when they do not represent a complete puzzle state.
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