The XY-Wing
Learn the XY-Wing: a three-cell pincer of bi-value cells that eliminates a shared candidate wherever the two pincers overlap.
The XY-Wing uses three cells that each have exactly two candidates. A pivot cell {X, Y} sees two "pincer" cells, {X, Z} and {Y, Z}, that share a third digit Z.
Whatever the pivot turns out to be, one of the pincers must become Z. So any cell that both pincers can see cannot be Z — and you remove it there.
It is the gateway to chain logic. The example highlights the pivot and its two pincers, and the candidate they jointly eliminate.
Practise the XY-Wing
The best way to learn a technique is to use it. Play a puzzle at the level where it first appears, or drop a tricky board into the solver to watch it in action.
Frequently asked questions
What is an XY-Wing?
Three bi-value cells forming a pincer: a pivot {X,Y} linked to {X,Z} and {Y,Z}. Cells seen by both pincers cannot be Z.
When should I try an XY-Wing?
On expert puzzles when fish patterns like the X-Wing run out. Look for a bi-value pivot whose two candidates each pair with a common third digit nearby.
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