- A Hidden Triple: 3 candidates confined to exactly 3 cells in a unit — remove all other candidates from those 3 cells
- A Hidden Quad: 4 candidates confined to exactly 4 cells — same rule
- Hidden subsets are often harder to spot than naked ones but just as powerful
- Look for units where 3–4 digits each appear in only 2–3 of the unit's cells
- Finding a Hidden Quad on an Expert puzzle is rare but often decisive
Quick Review: Hidden Singles and Pairs
A Hidden Single is the simplest hidden subset: one candidate confined to one cell in a unit — place it immediately. A Hidden Pair is two candidates confined to two cells — remove all other candidates from those two cells. Triples and Quads extend the same logic to larger groups.
What Is a Hidden Triple?
A Hidden Triple exists when three candidates (say 3, 7, and 9) can only appear in three specific cells within a unit. Those three cells may have other candidates too — but since 3, 7, and 9 can only go in these three cells, the three cells collectively "own" these candidates. All other candidates in those three cells can be eliminated.
Example: In a row, digits 3, 7, and 9 can each only appear in cells at positions 2, 5, and 8. Cells 2, 5, and 8 may also have candidates 1, 4, 6, and so on — but those can all be removed, because 3, 7, and 9 need the three cells and no room remains for anything else.
How to Find Hidden Triples
- Choose a unit (row, column, or box)
- List every candidate and which cells in that unit contain it
- Look for any 3 candidates that appear in only 3 (or fewer) of the cells
- If found, eliminate all other candidates from those 3 cells
Hidden Quads
The same logic with 4 candidates confined to 4 cells. Hidden Quads are rare and difficult to spot by eye, but they appear occasionally in Expert puzzles. In practice, if you find 5 candidates each confined to 5 or fewer cells in a unit, check whether 4 of those candidates are confined to only 4 cells — that is your Hidden Quad.
Naked vs. Hidden: Which to Look for First?
Naked subsets are usually easier to spot because you look at cells (what candidates does this cell have?) rather than digits (where can this candidate go?). Try Naked Pairs and Triples first, then switch perspective to look for Hidden subsets if naked ones don't appear. Both approaches cover the same logical ground from different angles. See the full techniques library for side-by-side comparisons.