How it works
An XY-Wing is a short chain that use 3 cells. The chain use 3 digits, symbolically called X, Y, and Z. The cell in the center is called pivot, the other 2 cells are called pincers The pivot contains candidates XY, and the pincers contain XZ and YZ respectively. This makes it possible to eliminate the candidate Z from all cells that can see both pincers.
In order to easier help players to recognize the patters, the XY-Wing have been divided into 2 subtypes.
Type 1 (box/line)
When one pincer share a row or column with the pivot, and the other share a box/section, it is a type 1 wing. It is possible to eliminate up to 5 candidates with this type.
Type 2 (row/column)
When one pincer share a row with the pivot, and the other share a column, it is a type 2 wing. Only one candidate can be eliminated in this case.
Example
This example shows a Type 1 Wing, the pivot is in r1c5, with the pincers in r1c2 and r2c6.
The numbers are defined as X = 1, Y = 5, Z = 9. As the cells r2c2 and r2c3 can see both pincers, we can remove the
candidates for 9 in those 2 cells (marked with red).
