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Sudoku technique · Subsets · first needed in Focused puzzles

Hidden triple

3 digits are restricted to the same 3 cells in a house. Those cells cannot contain other digits.

How to spot it

Track where selected digits can go, rather than looking for small candidate lists.

The common mistake

The selected digits must have no locations elsewhere in the house. Erase the other digits inside the chosen cells.

Learn this first

Candidates and the row / column / box rules.

A worked example

This position comes from SudokuByte’s lesson on the Hidden triple. Gold cells hold the evidence; green cells are the pattern’s ends.

The Hidden triple in this position
The result: pencil marks it removes, in red

  1. Where to look

    Track where selected digits can go, rather than looking for small candidate lists.

    3 digits are restricted to the same 3 cells in a house. Those cells cannot contain other digits.

  2. Read the evidence in this position

    In row 9, the digits 2, 3, 6 appear only in r9c3, r9c4, r9c5.

  3. Why the deduction must follow

    Those 3 digits need 3 different cells. These are their only 3 cells, so those cells have no room for an extra digit. Remove the other pencil marks inside them.

  4. Apply the result

    Erase 4 from r9c3, r9c4. Erase 5 from r9c3. Erase 9 from r9c3, r9c4, r9c5. The pattern may remove candidates without immediately solving a cell.
Practice the Hidden triple on a real boardPlay a Focused puzzle

More subsets

Further reading: hodoku.sourceforge.net