Naked Quad
Hard
Used by Smart Hint
Four cells in a unit whose candidates combine to exactly four digits — eliminate those digits elsewhere in the unit.
- Cells that establish the pattern
- Where the conclusion lands
- Candidate ruled out
How it works
- A3, C3, E3, and F3 only draw from {1, 3, 6, 7} between them — a Naked Quad spread across four cells with none holding all four.
- Since those four digits are locked into those four cells, remove 1, 3, 6, and 7 from the rest of the row — H3 keeps its 4 but loses the rest.