Wings

Wings combine candidates from a small number of cells. Their endpoints force a shared candidate to be true in at least one location, allowing that candidate to be removed from cells that can see every relevant endpoint.

When to look for it

Look for Wings when the grid has many bivalue or trivalue cells. They often appear before longer chains and ALS techniques.

Implemented in Xodoku

XY-Wing

An XY-Wing has a two-candidate pivot XY and two pincers XZ and YZ. Both pincers see the pivot. Candidate Z can be removed from cells that see both pincers.

XYZ-Wing

An XYZ-Wing has a three-candidate pivot XYZ and two pincers XZ and YZ. Candidate Z can be removed from cells that see the pivot and both pincers.

W-Wing

A W-Wing uses two identical bivalue cells. A strong link for one candidate connects the endpoints, allowing the other candidate to be removed from cells that see both endpoints.

Alias

WXYZ-Wing is recognized as a useful teaching name, but in Xodoku it is returned as an ALS shape when the proof is ALS-XZ-like.