W-wing
ExpertA W-wing starts with two cells holding the same pair, XY, that don’t see each other. If some row, column or box has exactly two places for X, one seeing each of the two cells, then one of the cells must be Y. A cell that sees both of them can’t be Y.
How to spot it
- Find two cells with the same two candidates, X and Y, that don’t see each other.
- Find a unit where X has exactly two places, one seeing each cell.
- Remove Y from every cell that sees both pair cells.
Why it works
One of the two places for X holds it, so the pair cell it sees isn’t X, which makes that cell Y.
Example
5
7
9
1
2
3
8
8
3
6
5
4
1
9
2
1
4
3
8
9
7
9
8
4
5
8
7
4
3
4
5
8
9
6
3
8
2
5
7
2
1
9
5
6
8
4
3
4
8
5
2
6
Look at the two cells holding the same pair, 1 and 6.
Common mistakes
- Using a unit where X has a third place: the link needs exactly two.
- Removing X instead of Y.