Hidden Triple
Three digits appear in only the same three cells of a unit, so every other candidate is cleared from those cells.
Rule
In a unit, x, y, z lie only in 3 cells → those 3 cells keep only {x, y, z}.
Find three digits with only three places
In box 2, the digits 1, 3 and 8 appear only in the three cells r1c4, r1c5 and r3c5.
The idea
The hidden pair extended: three digits need three places, and only three cells contain them. Those cells belong to these three digits; every other candidate in them goes.
Each digit does not have to appear in all three cells — it is enough that all their positions fit inside the three cells.
Hidden and naked sets always come together: in a unit with k empty cells, a hidden set of n cells matches a naked set of k − n cells in the rest. Look for whichever is smaller.
How to spot it
- Count the places of each digit in the unit; take the digits with 2–3 places and try grouping them in threes.
- This is the hardest technique at this level to spot by eye — use it when the others have run out.
Common mistakes
- Including a digit that has four places in the triple.
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Related techniques
References
The examples on this page are generated from random puzzles, not taken from these sources.