XY-Wing
A Sudoku solving technique · level 6 · first needed around SE grade 7
By The Hardest Sudoku Team · Last updated
TL;DR
An XY-Wing is a three-cell pattern (a pivot seeing two pincers) that forces a common digit out of any cell both pincers can see.
How does the XY-Wing work?
A pivot cell holds candidates {X,Y}; one pincer sees the pivot with {X,Z}, the other with {Y,Z}. Whatever the pivot turns out to be, one pincer becomes Z — so Z is eliminated from every cell that both pincers can see.
When does it apply?
When you can find a pivot with two candidates and two pincers that each share one candidate with the pivot plus a common third candidate Z.
A worked example
Pivot {2,5}, pincers {2,8} and {5,8}: any cell seeing both pincers cannot be 8, because one of the pincers must be 8.
See where this fits on the difficulty scale on the SE grade page, or browse every technique in the glossary.