Finned X-Wing
An X-Wing with one extra in-box candidate that narrows the cut.
Learn the Finned X-Wing Sudoku technique: an almost-X-Wing whose fin shares a box, so the digit is cut only from cells that see both the fish and the fin.
How to use it
- Spot the almost X-Wing. Find two rows (or columns) where a digit would form an X-Wing except that one of them has one or two extra spots — the fin — all inside a single box.
- Reason about the fin. If the fin is empty the X-Wing is real; if the fin holds the digit it sits in that one box. Either way the digit is committed near the fin’s box.
- Cut only where both apply. Remove the digit only from cells that the basic X-Wing would clear AND that also see every fin cell — in practice, the cover cell inside the fin’s box.