Sudoku techniques · Extreme
Finned X-Wing in Sudoku
A Finned X-Wing is an X-Wing that almost works. One base line carries an extra candidate, the fin, which breaks the clean elimination. But the fin is confined to one box, so candidates in that box which would be removed either way can still go.
Why it works
A fin is one extra cell on a base line that stops an X-Wing from being complete, so the candidate can be removed only from cells in the fin's box, outside the X-Wing corners and the fin, that lie on a crossing line through an X-Wing corner in that box.
How to spot it
Stop discarding near-misses. A row with three spots instead of two is often a finned pattern.
- Two of the three must line up with a clean pair in another row; the third is the fin.
- The fin must share a box with one of the X-Wing corners, or there is no elimination.
- Only cells inside the fin's box, on the relevant crossing line, are cleared: a much smaller payoff than a clean X-Wing, but free once you have looked.
Builds on
Worked example
These are the app's own lesson boards. Step through them the same way a hint does.
- 1
5 almost forms an X-Wing in two base rows. The fin is one extra cell in one of those rows that also has 5 as a candidate.
- 2
This X-Wing sits on two base rows. We can remove the candidate 5 only from cells inside the fin's box that lie outside the X-Wing corners and the fin, and that share a column with an X-Wing corner in that box.