X-Wing
A Sudoku solving technique · level 4 · first needed around SE grade 5
By The Hardest Sudoku Team · Last updated
TL;DR
An X-Wing is a rectangle pattern where a digit's candidates in two rows line up in the same two columns, allowing eliminations down those columns (or vice versa).
How does the X-Wing work?
When a digit appears as a candidate in exactly two cells of two different rows, and those cells sit in the same two columns, the digit forms a rectangle. It must occupy opposite corners, so it can be removed from those two columns everywhere else.
When does it apply?
When two rows (or two columns) each restrict a digit to the same two columns (or rows).
A worked example
If 6 appears only in columns 2 and 7 of both row 1 and row 5, then 6 is removed from columns 2 and 7 in all other rows.
See where this fits on the difficulty scale on the SE grade page, or browse every technique in the glossary.