- Look at the highlighted cells.
- Look at their notes: whichever way they are filled, the same notes are ruled out.
- So 9 can be removed from the crossed-out cells.
XYZ-Wing in sudoku
An XYZ-Wing is an XY-Wing whose pivot carries a third note. The pivot holds X, Y and Z. It sees two pincers: one holds X and Z, the other Y and Z. Every cell that sees all three cells, the pivot included, loses Z.
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How to spot it
Look for a cell with three notes that sees two cells with two notes each, both taken from its three and both containing the same number. The cells to clean up share a box with the pivot and a line with one pincer, so there are at most two of them.
Why it works
The pivot is X, Y or Z. If it is X, the first pincer must be Z; if it is Y, the second must be; otherwise the pivot itself is Z. One of the three cells is Z in every case, so a cell that sees all three cannot be.
On a real puzzle
This is XYZ-Wing on its practice puzzle, at the first step that needs it. The game's hint explains the step like this:
Practice it
No level of the game needs XYZ-Wing, so this practice puzzle is harder than Extreme, its hardest level. Fill in what you can, then look for the pattern, or ask for the hint: each game has one.