A Y-wing (XY-wing) uses three bi-value cells: a pivot and two pincers that share a digit no cell can escape.
Pivot and two pincers
The pivot holds (1,2). One pincer (1,3) shares a unit with it, the other (2,3) shares another. Whatever the pivot becomes, one pincer is forced to 3 — so any cell seeing both pincers cannot be 3.