A digit that lives in one row of a box

Look at one 3×3 box and one digit that is not in it yet. If that digit’s leftover cells in the box all sit in one row, the digit lives in that row of the box.

Then it cannot appear in the rest of that row, outside the box. Erase those notes. The same is true for a column.

The other way around works too. If a digit’s leftover cells in a row all sit in one box, the rest of that box cannot hold it.

This is the first extra idea after last empty cell, only-one-place, and only-one-digit. You still do not guess. How to play Sudoku names this step in one sentence. Play Sudoku and watch one box at a time.

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