XYZ-Wing
An XY-Wing whose middle cell has three candidates.
A technique for Expert puzzles. Play a Expert puzzle
What it does
Like an XY-Wing, but the pivot has three candidates, X, Y and Z, and the wings are X or Z, and Y or Z. Whatever the pivot holds, one of the three cells is Z: the pivot itself, or the wing that its digit forces to Z.
How to spot it
Look for a cell with three candidates, and two cells it sees with two candidates each, both including the same digit of the three. The pivot is the cell with three candidates.
What it lets you do
A cell that sees all three cells, the pivot and both wings, can’t be Z. Such cells sit in the pivot’s box, next to it, so look there.
Try it
Find the XYZ-Wing on this board. Pick the cells it clears, mark the candidates it removes, then check.
These are the notes after the easier steps: some candidates are already removed, as they would be in your game.
Practise it
The best way to learn a technique is to meet it in a real game. Practice puzzles are sure to need it, at Expert level; any Expert puzzle may need it too.