Y-Wing
Advanced Removes candidates Used in: Sudoku, Killer Sudoku
Also called the XY-Wing. A “pivot” cell with candidates {A,B} sees two “pincer” cells, one {A,C} and one {B,C}. Whichever value the pivot takes, one pincer is forced to C — so C can be eliminated from any cell that sees both pincers.
How to spot it
A bi-value pivot {A,B} that sees one {A,C} cell and one {B,C} cell.
What you can conclude
Eliminate C from any cell that sees both pincers.
Worked example
Pivot {1,2} sees pincers {1,3} and {2,3}. Whatever the pivot takes, one pincer becomes 3 — so 3 leaves any cell seeing both pincers.