X-Wing

A digit forms a rectangle across two rows and two columns.

Learn the X-Wing Sudoku technique: a digit boxed into a rectangle across two rows and columns lets you eliminate it elsewhere.

How to use it

1. Find two matching rows. Find a digit that appears as a candidate in exactly two cells of two different rows, and those cells line up in the same two columns.
2. Form the rectangle. The four cells form a rectangle. The digit must occupy one diagonal pair, so the two columns are spoken for.
3. Eliminate down the columns. Remove the digit from every other cell in those two columns (the same logic works swapping rows and columns).