XY-Wing
AdvancedUsed at: Hard
Three cells chain through three candidate digits. Starting from the middle cell (pivot), you can eliminate the common candidate of the two wing cells.
XY-Wing — Explained
XY-Wing links three cells through three digits: the pivot holds XY, one wing holds XZ, and the other holds YZ. No matter whether the pivot becomes X or Y, the shared digit Z must appear in one of the two wings, so any cell that sees both wings cannot contain Z.
When to Use
Useful in upper-intermediate to advanced puzzles when basic pair techniques stop making progress and you need a targeted elimination without a large fish pattern.
Common Mistakes
Choosing wings that do not both see the pivot, or eliminating Z from cells that do not see both wings. Visibility rules are the whole pattern.
Tips
Start by finding a bivalue pivot. Then look for two nearby bivalue wings that each share one digit with the pivot and one common elimination digit.
XY-Wing Steps
Find the pivot
Find a cell with exactly two candidates (XY). This is the pivot.
Find the wings
Find two cells sharing the same row/column as the pivot, one with XZ and the other with YZ.
Eliminate common digit
Eliminate Z from cells that see both wings.