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.
Once XY-Wings click, longer chains stop looking so intimidating. In the example, find the pivot first, then trace each pincer to 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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