XYZ-wing
ExpertAn XYZ-wing is an XY-wing whose pivot has a third candidate: the pivot holds XYZ, and it sees two pincers holding XZ and YZ. Now the pivot itself could be Z, so only a cell that sees all three cells loses Z.
How to spot it
- Find a cell with three candidates: the pivot, XYZ.
- Among the cells it sees, find one with XZ and one with YZ.
- Remove Z from cells that see the pivot and both pincers.
Why it works
If the pivot is X, the XZ pincer is Z; if it is Y, the YZ pincer is Z; if it is Z, it is Z itself. One of the three holds Z.
Example
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Look at these three cells.
Common mistakes
- Removing Z from cells that see only the pincers, as in an XY-wing: here they must see the pivot too.
- Using pincers that don’t both share Z with the pivot.