XY-Wing
A pivot cell and two "wing" cells, each sharing one candidate with the pivot, corner a shared digit out of any cell both wings can see.
How it works
- 1A1 is the pivot with candidates {1, 2}. E1 shares its row and candidate 1 (plus a 3); A5 shares its column and candidate 2 (plus that same 3).
- 2If A1 is 1, E1 can't be 1, so it must be 3. If A1 is 2, A5 can't be 2, so it must be 3. Either way, one of the wings is 3 — eliminate 3 from E5, which both wings can see.
- Cells that establish the pattern
- Where the conclusion lands
- Candidate ruled out