XY-Wing

Level: Advanced

Eliminates a shared number using a candidate chain between a pivot and two wing cells.

The XY-Wing uses three cells. It forms when there's a pivot cell with candidates {X,Y}, and two wing cells {X,Z} and {Y,Z} that both see the pivot.

Whether the pivot turns out to be X or Y, one of the two wings is forced to be Z. So in any cell that both wings can see, you can eliminate Z.

It's an introductory chaining technique that builds your ability to read the relationships between candidate cells.

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