A naked quad involves four cells in a house that contain only candidates from a set of four digits.
Understanding the Concept
Four cells collectively contain only four different candidates.
Like triples, not every cell needs all four candidates.
Various combinations are possible: {1,2,3,4}, {1,2}, {3,4}, {1,3,4}, etc.
These four digits are locked to these four cells.
Eliminate these four candidates from all other cells in the house.
Naked quads are rare and hard to spot due to many subset combinations.
Examples
Naked Quad in Column
Four cells in this column contain only digits from {1, 3, 6, 9}. One has {1,9}, another {3,6}, another {1,3,6}, and the last {6,9}. Eliminate 1, 3, 6, 9 from all other cells in the column.
5
7
123456789
2
4
5
7
4
2
4
123456789
5
7
2
5
7
4
7
2
5
5
7
123456789
2
4
2
7
5
4
123456789
2
7
5
4
2
Pattern / InvolvedEliminated
Pro Tips
- •Quads are rare - don't spend too much time hunting for them
- •Usually easier to find the complementary hidden pattern instead
- •In a house of 9 cells, a naked quad implies a hidden quint (5 cells)
- •Computer solvers find these easily; humans struggle
