W-Wing
Two identical bi-value cells connected by a strong link on one of their digits.
What it is
A W-Wing uses two cells with the same two candidates, say {X,Y}, that do not see each other. They are connected by a unit in which X has exactly two candidate cells, one seeing each of the pair. If both {X,Y} cells were X, that connecting unit would be contradicted — so at least one of them is Y. Any cell seeing both can therefore drop Y.
How to spot it
Find two cells with identical pairs of candidates in different units. Then look for a row, column or box where one of their two digits has exactly two candidates, positioned so that each sees one of the pair. The other digit is what you eliminate from cells seeing both.
Worked example
Step through the reasoning below. Each step adds one layer: first the position, then the pattern, then the candidates involved, and finally what can be eliminated.
Step 1 of 4: The starting position
- Pattern cells
- 2/2, 5/3, 8/2, 8/3
- Digits
- 6, 9
- Eliminations
- 2/3
Press a marked square to point it out on the board above.
Why it matters
The W-Wing is elegant and surprisingly common once you know the shape. It often applies where XY-Wings do not, because the two key cells can sit far apart on the board.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
What is a strong link?
A unit in which a digit has exactly two possible cells. One of the two must be true, which is precisely the leverage the W-Wing needs.
Must the two cells be in the same row or column?
No. They must not see each other at all. The connection is made entirely by the strong link between them.
Put it to use
Where you will meet it
Expert grids are the only place this pattern regularly decides the solve. Bring your notes.
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