XY-Wing

An XY-Wing uses a pivot cell with two candidates, X and Y, and two “wings”: one that sees the pivot and holds X and Z, another that sees the pivot and holds Y and Z. Whatever the pivot turns out to be, one wing becomes Z, so any cell that sees both wings can’t be Z.

How to spot it

1. Find a cell with exactly two candidates, X and Y. This is the pivot.
2. Find a cell that sees the pivot with candidates X and Z, and another that sees it with Y and Z.
3. Remove Z from every cell that sees both wings.

A real example

The pivot r9c7 is 2 or 7. If it’s 2, then r9c4 (2/1) must be 1. If it’s 7, then r3c7 (7/1) must be 1. Either way one wing is 1, so any cell that sees both can’t be: r3c4 loses 1.

Tips

• All three cells must have exactly two candidates.
• The two wings don’t need to see each other. The eliminated cell must see both.

Practice on Expert puzzles