Box-Line Reduction

A digit confined to one line within a box clears the box.

Learn Box-Line Reduction in Sudoku: when a digit on a line only fits one box, eliminate it from the rest of that box.

How to use it

1. Find a line-locked digit. In a row or column, find a digit whose only candidate cells all fall inside a single 3×3 box.
2. Reduce the box. The digit must lie on that line, so within the box it can only be in those line cells.
3. Eliminate elsewhere in the box. Remove the digit from the other cells of that box.