Locked Triple

Also called Locked Naked Triple, Intersection Triple.

New to this shorthand? How to read a sudoku grid explains r4c7, houses, candidates and the rest.

What it means

A triple that sits in two groups at once, usually a row and a box. The three digits clear out of both groups, which is why it is worth spotting.

The exact rule, for stronger players

The rule, stated exactly: A Naked Triple whose three cells all lie in the same box and the same line. The elimination applies in both houses.

What it removes: Remove all three digits from all other cells of the box and of the line.

Why it works: As for the locked pair. The subset argument is house-local, so a subset occupying two houses eliminates in both.

Worked examples

These come from real Proven Sudoku boards. Nobody drew them by hand to make the pattern look neat. Each one is checked first, so the board is one you could really meet, the pattern is really there, and every digit it rules out is really wrong.

r7c9, r8c9, r9c9 hold only 1, 2, 8 and share c9 and b9, so those digits are removed from both houses at once.

r4c1, r4c2, r4c3 hold only 1, 2, 5 and share r4 and b4, so those digits are removed from both houses at once.

Learn these first

Naked TripleThree squares in one group share the same three digits between them.
Locked PairA pair that shares two groups at once, usually a row and a box.

Related subsets

Naked PairTwo squares in the same group both hold only the same two digits.
Naked QuadFour squares in one group share the same four digits between them.
Naked Subset (general form)Find some squares in one row, column or box.
Hidden PairTwo digits in one group can only go in the same two squares.
Hidden QuadFour digits in a group can only go in the same four squares.

How often does it come up?

Our rough estimate: less common than the locked pair, since three cells must share a box and a line.

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