Sudoku solving technique · Expert
Finned X-Wing
An X-Wing with extra cells, the fins, inside one box.
What is a Finned X-Wing?
A Finned X-Wing is an X-Wing with extra cells. In one row, a candidate appears in only two cells. In a second row, it appears in the same two columns plus one or more fins, which all lie in the block of one of that row's two corners. If no fin holds the candidate, the X-Wing applies; if a fin holds it, no other cell in that block can. Either way, it can be eliminated from the cells of that corner's column that lie in the fin block, outside the two rows. The same works with columns instead of rows.
How to spot a Finned X-Wing
You find almost an X-Wing: in one row the digit fits in only two cells, in the second row it fits in the same two columns plus one or more cells that all lie in the box of one corner. You only remove the digit where both cases agree: in that corner’s column, inside the fin box, outside the two rows. The same works with columns instead of rows.
- Difficulty
- In Sudoku Pro, this technique belongs to the Expert level.
- Learning path
- Technique 17 of 20 on the learning path
An example from the app
| Empty | Empty | Empty | Empty | Empty | Empty |
| Empty | Empty | Empty | Empty | Given 3 | Empty |
| Empty | Affected cell (orange). Candidates 1, 3, 4, 6. Eliminated 2 | Empty | Empty | Empty | Empty |
| Given 5 | Pattern (purple). Candidates 1, 2, 6 | Pattern (purple). Candidates 1, 2, 6 | Given 4 | Pattern (purple). Candidates 1, 2, 6 | Given 3 |
| Given 1 | Pattern (purple). Candidates 2, 5 | Given 4 | Given 3 | Pattern (purple). Candidates 2, 5 | Given 6 |
| Empty | Empty | Empty | Empty | Empty | Empty |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Affected cell (orange)