Wings Techniques

XY-Wing

Here is an XY-Wing with R2C7 = {26}, R3C8 = {24}, R2C5 = {46}. Whichever the value of R2C7 (the pivot), there must be a 4 either in R3C8 or in R2C5 (the pincers). Therefore neither R2C9 nor R3C5 may hold 4 (nor could R3C46 & R2C8).

XYZ-Wing

Here is an XYZ-Wing with R5C6 = {349}, R5C1 = {34}, R6C4 = {39}. Whichever the value of R5C6, there must be a 3 in one of these three cells -> R5C4 cannot hold 3 (nor could R5C5). Unlike the XY-Wing pattern, here we cannot eliminate 3 from R6C12.

WXYZ-Wing

The WXYZ-Wing is an extension of the XYZ-Wing to 4 cells with 4 candidates, which can be generalized to N cells with N candidates. JSudoku will catch all these using Almost Locked Sets: ALS-XZ.

Y-Wing Style alias W-Wing alias Semi Remote Pair

A Y-Wing is a simple pattern formed by a strong link and two cells with two same candidates. Here is a Y-Wing with a strong link on 2 in R7C56 and two cells R2C6 & R4C5 with {26}. Whichever the location of the 2 in R7, there must be a 6 either in R2C6 or in R4C5. Therefore R2C5 & R56C6 cannot hold 6 (nor could R13C5 & R4C6).


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