If three digits in a unit can only occupy three cells, they form a hidden triple: clear all other candidates inside those three cells.
What Are Hidden Triples?
A hidden triple occurs when three digits in a row/column/box appear only in three cells of that unit (those cells may still display extra candidates). In that case, you can remove every other candidate from those three cells.
Step-by-Step Example
1) Digits like {4,5,6} repeat near the center.2) Check the row: the set is confined to three positions.3) Check the column: the same three cells remain ⇒ hidden triple.4) Since it’s a hidden triple, clear other candidates within those three cells; direct placements often follow.
Where It Works
Any row,
Any column,
Any 3×3 box.
Hidden vs Naked
With hidden triples you prune inside the three cells; with naked triples you eliminate those digits from the rest of the unit.
