Naked Triple
Three cells in a unit whose candidate sets together cover only three digits. Lock those digits in; prune them from the rest.
Advanced sudoku technique
What it is
A naked triple extends the naked-pair idea to three cells. The three cells don't all need the same three candidates — they just need to be subsets of the same three-digit set. The common shapes are {a,b,c}/{a,b,c}/{a,b,c}, {a,b,c}/{a,b}/{b,c}, and the slightly trickier {a,b}/{b,c}/{a,c}. Whatever permutation of the three digits ends up in those three cells, no other cell in the unit can hold any of them. Naked triples often unlock the next chain of singles.
When to use it
When singles, pointing, claiming, and naked pairs have all gone quiet. Inspect each unit for three cells whose combined candidate union has exactly three distinct digits.
Worked example
In column 3, three empty cells have candidates {2, 5}, {5, 8}, and {2, 8}. Their union is {2, 5, 8} — exactly three digits across three cells. Whatever permutation places 2, 5, and 8 into those cells, every OTHER empty cell in column 3 must drop 2, 5, and 8 from its candidates.
Try it
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