X-Wing

Intermediate

A digit confined to the same two columns across two rows forms a rectangle; it can be eliminated from those columns in all other rows.

How It Works

When a digit appears in exactly two columns across two rows, it forms a rectangle. The digit must occupy two diagonally opposite corners, so it can be eliminated from those same two columns in all other rows.

The same logic applies column-wise: two rows and two columns form the X-Wing.

X-Wing is the foundation of the larger "fish" techniques (Swordfish, Jellyfish).

Example

3
15
24971
35
6
6
45
13825
56
4
14
5
67
28
34
19
26
5
37
8
25
31752
57
9
9
58
46387
59
2
7
35
89634
15
1
26
5
39
17
24
36
18
5
27
4
56
78143
25
6
1
45
62519
58
8
Key cells of the techniqueCells where elimination is appliedCandidate to be placedEliminated candidate (crossed out)

Digit 7: In Row 2 only at C3 and C7; in Row 8 only at C3 and C7 → Eliminate 7 from columns 3 and 7 in all other rows.

Practice with a Real Puzzle

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

Medium26 givensStrict