Techniques / Wings
XY-Wing
A pivot with candidates {X,Y} and two pincers {X,Z} and {Y,Z}.
Find a cell with exactly two candidates, X and Y (the pivot). It sees two other bi-value cells: one with X and Z, another with Y and Z (the pincers).
If the pivot is X, the first pincer becomes Z. If the pivot is Y, the second pincer becomes Z. Either way one pincer is Z, so Z can be removed from any cell that sees both pincers.
Notation
XY-Wing: 2 can be removed from r3c4.
pattern fin / link removed
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