Learn / Wings
Sudoku technique · Wings · first needed in Expert puzzles
W-Wing
Two cells with the same pair are connected through a strong link on one of their digits. Their other digit is guaranteed at one end.
How to spot it
Look for matching bivalue cells and a two-location bridge.
The common mistake
Two matching pairs by themselves are not a W-Wing. Verify the bridge and both endpoint connections.
Learn this first
Strong links and XY-Wing.
A worked example
This position comes from SudokuByte’s lesson on the W-Wing. Gold cells hold the evidence; green cells are the pattern’s ends.
2
8
4
7
1
9
3
6
25
27
3
5
6
4
8
1
29
29
1
9
6
3
2
5
4
8
7
359
2
9
49
8
1
6
7
349
4
6
7
5
3
2
8
19
9
39
1
89
49
7
6
5
29
2349
9
7
19
8
5
3
2
4
6
6
5
2
1
9
4
7
3
8
8
4
3
2
6
7
9
5
1
2
8
4
7
1
9
3
6
25
27
3
5
6
4
8
1
29
29
1
9
6
3
2
5
4
8
7
359
2
9
49
8
1
6
7
349
4
6
7
5
3
2
8
19
9
39
1
89
49
7
6
5
29
2349
9
7
19
8
5
3
2
4
6
6
5
2
1
9
4
7
3
8
8
4
3
2
6
7
9
5
1
Where to look
Look for matching bivalue cells and a two-location bridge.Two cells with the same pair are connected through a strong link on one of their digits. Their other digit is guaranteed at one end.
Read the evidence in this position
r2c9, r6c8 both contain 2, 9. The connecting strong link on 9 lies in row 5.Why the deduction must follow
One bridge endpoint must contain 9. It excludes 9 from the wing it sees, forcing that wing to be 2. Which bridge endpoint is true does not matter: one wing supplies 2, so candidates seeing both wings lose 2.Apply the result
Erase 2 from r2c8, r6c9. The pattern may remove candidates without immediately solving a cell.
Further reading: hodoku.sourceforge.net