Hello and welcome to the XY wing technique course!
The XY wing technique is a technique that is often compared to the hooks of an eagle and its prey. The objective is to find the hook cells and proceed to eliminate the prey.
The XY wing technique
First, we start by finding a column with a cell having only two candidates, called pivot. The candidates in the cell are called X and Y. In the example below, the pivot is cell R5-C5.
The R2-C1 and R9-C3 cells are clamps.
All companion cells in R2-C1 and R9-C3 clamps cannot contain a 3. In this case, it is safe to delete candidates from cells containing a 3.
Cells R2-C3 and R3-C3, with candidate 3 deleted, are in the same house of both R2-C1 and R9-C3 clamps.
How do you find the XY wings?
The XY wings must involve three companion cells that have only two candidates each, so start by looking for three companion cells that have only two candidates.
Once found, make sure the candidates follow the XY, XZ and YZ rule.
If you find this scenario, look for companion cells in XZ and YZ cells, and eliminate the Z candidates from them.