Tier 3 · first asked for by Tough
Y-Wing
A pivot cell and two pincers force a digit into one of the pincers, clearing it from what both see.
Also called Y-Wing, XY-Wing, Bent Triple.
Find three cells with exactly two candidates each: a pivot holding {X,Y}, and two pincers that the pivot can see, holding {X,Z} and {Y,Z}.
The pivot is either X or Y. If it is X, the first pincer cannot be X, so it is Z. If it is Y, the second pincer must be Z. Either way one of the pincers is Z — so Z can be removed from every cell that both pincers can see.
The elegance is that you never learn which pincer it is, and never need to. Both branches lead to the same conclusion, which is what makes this reasoning rather than guessing.
A worked example
A real position, with the pencil marks a solver would have at that point.
the pattern · what it rules out · 5 a candidate that goes
What it proves. Y-Wing: pivot R2C6 (13) with pincers R2C8 and R2C9 forces one pincer to be 8, so 8 leaves R3C8, R3C9.