XY-Wing

Level: first needed in Extreme puzzles. In one line: Three two-candidate cells (a pivot and two pincers) remove a number from cells that see both pincers.

An XY-Wing (also called a Y-Wing) uses three cells that each have exactly two candidates. The pivot has {X, Y}. It sees two pincers: one with {X, Z} and one with {Y, Z}.

If the pivot is X, the first pincer must be Z. If the pivot is Y, the second pincer must be Z. Either way, one of the pincers is Z. So any cell that sees both pincers cannot be Z, and Z can be removed from it.

Example from a real puzzle

This position comes from an Extreme puzzle in Sudoku Arena, at the exact moment the XY-Wing is the next logical move. Cells are named by row and column: R3C4 means row 3, column 4.

Cells that form the patternCandidate you can remove

XY-Wing with pivot R7C8 removes 3 from cells seeing both R7C5 and R8C9. Result: remove 3 from R7C9, 3 from R8C5.

Play this puzzle and look for the move yourself. It's a practice game, so it doesn't count towards your stats.

How to spot it

  1. Look for cells with exactly two candidates.
  2. Pick one as the pivot, say {X, Y}, and look for two cells it sees: one {X, Z} and one {Y, Z} (the same Z).
  3. Find the cells that see both pincers and remove Z from them.

Tips

  • "Sees" means shares a row, column or box.
  • The pincers don't need to see each other; they only need to share Z.

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