Finned X-Wing

Hard

X-Wing with extra "fin" cells in one row; eliminations are restricted to cells seeing the fin's box corner.

How It Works

Almost an X-Wing, but one row has extra candidate cells ("fins"). Eliminations still occur, but only for cells that see both the normal X-Wing corner AND all fin cells (i.e., in the same box as the fin).

The fins restrict the elimination scope but the technique still works.

Example

731849625
4
12
5
673
5
18
9
9
26
85
12
1
23
47
36
65
27
9
13
14
15
8
27
8
19
37
2
13
17
45
46
13
1
49
5
7
38
6
5
5
24
3
27
46
15
24
9
67
8
5
17
94
26
27
23
16
2
48
46
3
16
18
47
5
17
Key cells of the techniqueCells where elimination is appliedCandidate to be placedEliminated candidate (crossed out)

Digit 5: Row 2 at C3,C7; Row 8 at C3,C7,C9(fin). → Eliminate 5 only from cells seeing R8C7 (X-Wing corner) and also in the same box as R8C9 (fin).

Practice with a Real Puzzle

This 9×9 puzzle is solver-verified to require this technique on its solution path.

Hard24 givensStrict