Hidden pair

A worked example

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

1. Where to look

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

   2 digits are restricted to the same 2 cells in a house. Those cells cannot contain other digits.

2. Read the evidence in this position

   In box 2, the digits 8, 9 appear only in r1c6, r2c6.

3. Why the deduction must follow

   Those 2 digits need 2 different cells. These are their only 2 cells, so those cells have no room for an extra digit. Remove the other pencil marks inside them.

4. Apply the result

   Erase 2 from r1c6, r2c6. Erase 3 from r1c6. Erase 5 from r1c6, r2c6. The pattern may remove candidates without immediately solving a cell.