XY-Wing (Y-Wing)
A pivot of two candidates with two wings sharing one each — the digit they have in common falls anywhere seeing both.
How it works
- 1Find a cell with exactly two candidates {x,y} — the pivot — and two cells that see it with candidates {x,z} and {y,z}.
- 2Whichever the pivot turns out to be, one of the wings is forced to z.
- 3So z is impossible in any cell that sees both wings. Strike it there.