In this technique, four cells are used that contain four numbers. For any choice made in the hinge (cell B1 in the example below), one of the other cells will contain “z“, which can be excluded from the positions marked in red. Again, the “Z” numbers can be excluded from the cells that see the four “Zs“.
Example:
Another example:
There is also the possibility that the “Z” is not present in the hinge or in one of the other three cells.
There are other configurations for the WXYZ-Wing, but all are examples of the Almost Locked Set (ALS) technique, which will be seen later and much easier than trying to find within a Sudoku than the configurations below.
For any choice made in C1, we will have the “z” in one of the green positions:
For any choice in A1, we can eliminate the “Z” marked in red.
