What is XYZ-Wing? How to Solve Sudoku

What it is

A cousin of the XY-Wing where the pivot has three candidates (1, 2, 3). A is 1 or 3, and B is 2 or 3.

If the pivot is 1, A is 3. If it's 2, B is 3. Otherwise the pivot itself is 3.

One of the three cells is always 3, so any cell that sees all three can't be 3.

How to spot it

Start from a three-candidate cell and look for two cells it sees, each holding two of its candidates.

Example

Yellow cells are where to look, orange cells are the reason, red digits are candidates you can remove, and the blue digit is the answer.

R3C2 can be 1, 7, or 6. If it's 1, R3C1 is 6; if it's 7, R8C2 is 6; otherwise R3C2 itself is 6. One of the three is always 6, so any cell that sees all three (R1C2) can't be 6.