Naked quad
Four cells in the same house have just four different candidates between them. Those digits are reserved for the quad.
In row 1, the 4 highlighted cells can contain only the digits 2, 6, 8 and 9. These digits must fill those cells in some order, so remove these candidates from the other cells in row 1.
What to look for
Find four cells in one house whose candidates, taken together, are exactly four digits. The cells do not need identical candidate lists. The hints only point out naked quads in rows and columns.
Why it works
The four cells must contain those four digits in some order. No other cell in the house can contain any of them.
Try it step by step
- Choose four cells in the same house.
- Check that they have exactly four different candidates between them.
- Remove those digits from every other cell in the house.
Try it on a real puzzle
Start with the highlighted step, then keep solving. Use "Apply hint" to make the suggested change, or enter your own digits and candidate notes. Use "Undo" to reverse your last change.
| C1 | C2 | C3 | C4 | C5 | C6 | C7 | C8 | C9 | |
|---|---|---|---|---|---|---|---|---|---|
| R1 | |||||||||
| R2 | |||||||||
| R3 | |||||||||
| R4 | |||||||||
| R5 | |||||||||
| R6 | |||||||||
| R7 | |||||||||
| R8 | |||||||||
| R9 |
Use the arrow keys to move, 1-9 to enter a digit and Backspace or Delete to clear a cell. To add or remove a candidate, press C and then 1-9.
Source puzzle number: 102536 · Play this puzzle from the start
A simple example
The candidate sets {1, 2}, {2, 3}, {3, 4} and {1, 4} form a naked quad when the four cells share a house.
A house is a row, column or 3 × 3 box. A line is a row or column. Two cells "see" each other when they share a house. R1C3 means row 1, column 3. Boxes are numbered 1-9 from left to right and top to bottom. Braces such as {1, 2} show a cell's candidates, not confirmed digits.