Sudoku solving technique · Pro
W-Wing
Two matching two-candidate cells, joined by a digit that appears only twice in a unit.
What is a W-Wing?
A W-Wing uses two cells with exactly the same two candidates that do not see each other. In a row, column, or block, one of these candidates appears in only two cells, one seeing each cell of the pair. One of those two cells must hold that candidate, so at least one cell of the pair holds the other one. The other candidate can be eliminated from any cell that sees both cells of the pair.
How to spot a W-Wing
Start with two cells that hold exactly the same two candidates and do not see each other. Then look for a row, column or box where one of the two digits appears in only two cells, one seeing the first pair cell and the other seeing the second. The other digit of the pair can be removed from cells that see both pair cells.
- Difficulty
- In Sudoku Pro, this technique belongs to the Pro level.
- Learning path
- Technique 13 of 20 on the learning path
An example from the app
| Given 4 | Pattern (purple). Candidates 1, 3 | Pattern (purple). Candidates 1, 3 | Given 2 |
| Empty | Empty | Empty | Pattern (purple). Candidates 3, 4 |
| Given 1 | Pattern (purple). Candidates 3, 4 | Given 2 | Affected cell (orange). Candidates 3. Eliminated 4 |
| Empty | Empty | Empty | Given 1 |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Affected cell (orange)