Naked Triples in Sudoku: Three-Cell Candidate Lock Guide

What is a Naked Triple?

A Naked Triple is the three-cell big brother of the Naked Pair. It appears when three cells in the same unit (row, column, or 3×3 box) contain, between them, only three different candidates.

1. Each of the three cells can only take one of those three digits.
2. Three cells, three digits: all three digits must be used up by exactly these cells.
3. The cells do not need all three candidates each. {1, 3}, {1, 2, 3} and {2, 3} still form a valid triple.
4. Therefore, those three digits cannot appear anywhere else in that unit!

Worked Example: Naked Triple in Row 1 Eliminates 2 from Cell R1C8

Look at the empty cells of Row 1 on the board below:

• The three locked cells: R1C2 holds {1, 3}, R1C4 holds {1, 2, 3}, and R1C9 holds {2, 3}. Together they use only the digits 1, 2 and 3.
• No smaller lock: No two of these cells share just two digits, so this is a true triple, not a hidden Naked Pair.
• The Triple Lock: Row 1 needs a 1, a 2 and a 3, and these three cells can hold nothing else. So 1, 2 and 3 are claimed by R1C2, R1C4 and R1C9.
• Target Elimination at R1C8: Cell Row 1, Column 8 (R1C8) has candidates {2, 8}. Because the triple claims Row 1's 2, candidate 2 is eliminated from R1C8, leaving 8 as a Naked Single!
• Bonus elimination: R1C3 {3, 7, 8} also loses its 3.