XY-Wing uses three cells with two candidates each to make eliminations.
Understanding the Concept
Involves three bi-value cells (cells with exactly 2 candidates).
The pivot cell sees both wing cells and shares one candidate with each.
If pivot is {X,Y}, one wing is {X,Z}, and other wing is {Y,Z}.
Any cell seeing both wings cannot contain Z.
Called XY-Wing because the pivot contains X and Y.
Very powerful technique that's easier to spot than fish patterns.
Examples
XY-Wing Example
Pivot R5C5={3,7}, Wing1 R5C2={3,9}, Wing2 R3C5={7,9}. Any cell seeing both R5C2 and R3C5 cannot be 9.
Pro Tips
- •Look for bi-value cells (exactly 2 candidates)
- •Find a pivot that sees two other bi-value cells
- •Check if the pattern matches XY-Wing structure
- •The elimination affects cells seeing both wings
