Naked Quad
Four cells in a row or column whose candidates combine to exactly four values — eliminate those values elsewhere in the line.
How it works
- 1The first four cells of this 6-cell row use candidates drawn entirely from {1, 2, 3, 4}.
- 2Those four values must fill those four cells. A Naked Quad does not require every cell to show all four candidates — only their combined set matters.
- 3So neither of the last two cells can be 1, 2, 3 or 4. Strike those, and both are left holding 5 or 6.
- 4Two spare cells rather than one is what keeps this a quad: with a single cell left over it would be solved outright, and asking where the 5 goes would have found it first.
- Candidates this technique rules out
- Cells read together — The connecting line shows which cells combine to make the deduction.
- Conclusion — The coloured candidate, or the final arrow when it lands outside the pattern, shows the result.