Hidden Triple
Three digits confined to the same three cells of a unit, no matter what else those cells show.
What it is
A hidden triple exists when three digits can each only be placed in the same three cells of a unit. Those cells must therefore hold exactly those digits, and every other candidate in them can be removed. As with hidden pairs, the cells may carry many extra pencil marks, which is what conceals the pattern.
How to spot it
For each digit missing from a unit, list the cells that could take it. Look for three digits whose possible cells all fall inside the same set of three. The digits do not each need all three cells — two of them is enough, as long as no digit escapes the set.
Worked example
Step through the reasoning below. Each step adds one layer: first the position, then the pattern, then the candidates involved, and finally what can be eliminated.
Step 1 of 4: The starting position
- Pattern cells
- 1/5, 1/6, 1/9
- Digits
- 1, 2, 7
- Eliminations
- 1/5, 1/6, 1/9
Press a marked square to point it out on the board above.
Why it matters
Hidden triples are rare but decisive: they can strip four or five candidates from a unit at once. They usually appear in dense units where nothing else works, and finding one often finishes a difficult section of the grid.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
How is this different from a naked triple?
A naked triple is spotted by looking at cells and their candidates. A hidden triple is spotted by looking at digits and where they can go. The eliminations happen in different places: naked triples clear the rest of the unit, hidden triples clear the three cells themselves.
Are hidden triples worth hunting for?
Only once simpler techniques are exhausted. They take real effort to find, but on expert puzzles they are sometimes the only available move.
Put it to use
Where you will meet it
Hard grids are built around moves like this one. That is where it earns its keep.
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