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XY-Wing

When one pivot and two wings remove a shared candidate.

Explanation

An XY-Wing starts with a two-candidate pivot. Two peer cells each share one pivot candidate and both contain the same third candidate. Any cell that sees both wings cannot contain that shared third candidate.

XY-Wing example Sudoku board 2 9 8 7 6 1 4 4 7 6 5 3 2 8 1 3 5 9 7 2 6 7 3 9 4 5 5 4 3 9 8 9 6 1 8 5 4 2 3 6 7 2 1 5 2 3 6 4 9 4 5 1 7
An example board where XY-Wing applies

Practice tip

Scan for two-candidate cells first. Then check whether two peers form matching wings around the pivot.

Example steps

  1. Find a pivot cell with candidates X/Y.
  2. Find one peer with X/Z and another peer with Y/Z.
  3. Remove Z from cells that see both wing cells.

Try this technique on a real puzzle.

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