XY-Wing in Sudoku: How to Spot It
Learn the XY-Wing Sudoku technique: a pivot cell and two wing cells force a shared candidate elimination.
Guided example
See the XY-Wing on this board
Read this as one teaching unit: first identify the active unit, then the marked pattern cells, then the candidates removed or maintained.
Quick answer
An XY-Wing in Sudoku uses a pivot cell with candidates X/Y and two wing cells X/Z and Y/Z. Any cell that sees both wings cannot contain Z.
How to spot it
Follow the board in order
- 1 Find a bivalue pivot cell with two candidates, such as 1 and 2.
- 2 Find one wing that sees the pivot and contains 1 plus a shared candidate, such as 1 and 7.
- 3 Find another wing that sees the pivot and contains 2 plus the same shared candidate, such as 2 and 7.
- 4 Remove the shared candidate from any cell that sees both wings.
What is an XY-Wing?
An XY-Wing is a three-cell candidate pattern. One cell is the pivot, and two cells are wings.
The pivot has candidates X and Y. One wing has X and Z. The other wing has Y and Z. The shared candidate Z is the number that can be eliminated from cells seeing both wings.
When to look for it
Look for XY-Wings after pairs and X-Wing scans stop helping. They are easier to spot if you first mark bivalue cells — cells with exactly two candidates.
Start with one bivalue pivot, then ask whether it sees two other bivalue cells that share a third candidate.
Example walkthrough
This walkthrough uses a real hard app puzzle tagged XY-Wing. The blue cells form a pivot-and-wings pattern with candidates 46, 45, and 56. Whichever value the pivot takes, one wing forces 5, so the shared peer r3c2 cannot keep candidate 5.
Why the elimination works
The pivot has only two possibilities. Each possibility forces the opposite wing toward the shared candidate.
Because both pivot branches force a 7 in one of the wings, any cell that sees both wings would conflict if it also contained 7.
XY-Wing vs. XY-Chain
An XY-Wing is the shortest useful XY-chain shape: pivot plus two wings.
An XY-Chain extends the same bivalue-link idea through more cells.
Common mistake
Do not eliminate the shared candidate from every cell in the same row or box. Only remove it from cells that see both wing cells.
FAQ
What is an XY-Wing in Sudoku?
An XY-Wing is a three-cell pattern with one pivot and two wings that eliminates a shared candidate from cells seeing both wings.
Do all three XY-Wing cells need two candidates?
Yes. The classic XY-Wing uses three bivalue cells.
What is the pivot in an XY-Wing?
The pivot is the bivalue cell that sees both wings and contains the two non-shared candidates.
What candidate is removed?
Remove the candidate shared by the two wings from any cell that sees both wing cells.
In this lesson
- Board example: see the pattern first.
- Walkthrough: connect each highlight to the rule.
- FAQ: check edge cases after the move is clear.
Practice this technique in Sudoku Coach
Read the pattern, then practice it step by step with guided hints that explain why the move works.
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