Box Brain Sudoku
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Expert · technique 17 of 18
Naked Quad
Four cells in a house hold only four digits between them.
How it works
Those four digits must fill those four cells, so remove them from the rest of the house.
A worked example
Naked Quad: in box 8, the cells in row 7, column 5; row 7, column 6; row 8, column 6 and row 9, column 6 can only hold 1, 4, 5 and 8, so those digits are removed from the rest of the house.
- The area to look at
- The cells that make the pattern
- Candidates it rules out
A real position from a puzzle in the app. Small digits are the candidates the step looks at; coloured digits are already solved.
Practise it in Box Brain Sudoku
The app teaches Naked Quad on this same board, then hands you puzzles that need it. When you are stuck mid-game, a hint first points you to the right area, then names the technique and shows the move.