Claiming / box-line reduction

A worked example

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

1. Where to look

   Start with a full row or column, then follow it into its one available box.

   A line needs a digit and all its available locations are in one box. Remove that digit from the rest of the box.

2. Read the evidence in this position

   In row 5, all remaining 1 candidates are r5c7, r5c8. All are also in box 6.

3. Why the deduction must follow

   row 5 must get its 1 from these cells. Wherever that 1 lands, box 6 already has its one 1. Its other cells outside row 5 therefore cannot contain 1.

4. Apply the result

   Erase 1 from r6c8. The pattern may remove candidates without immediately solving a cell.