A hidden quad occurs when four digits are confined to the same four cells in a house.
Understanding the Concept
Four specific digits can only appear in four specific cells within a house.
These cells usually contain additional candidates, hiding the quad.
Once found, remove all other candidates from these four cells.
Hidden quads are extremely rare and difficult to spot.
Often it's easier to find the complementary naked quint (5 cells).
Most puzzles can be solved without finding quads.
Examples
Hidden Quad Theory
If digits 2, 4, 6, 8 only appear in four specific cells of a box, those cells can only contain these even digits.
Pro Tips
- •Hidden quads are extremely rare in practice
- •Usually indicates you've missed an easier technique
- •Consider looking for other patterns first
- •More of theoretical interest than practical use
