W-Wing
Two matching bi-value cells joined by a strong link on one digit eliminate the other digit from cells seeing both.
A W-Wing uses two bi-value cells that share the same pair {x,y}, connected by a conjugate pair (strong link) on one of the digits. If a unit elsewhere allows x in only two cells, and each of those cells sees one of the bi-value cells, then y is forced into one of the two bi-value cells — so y can be eliminated from any cell that sees both.
It is a clean, symmetric pattern that often replaces a longer chain.
How to spot it
Find two cells with the identical pair {x,y} that do not see each other. Look for a unit where x is a conjugate pair (only two candidates), with one candidate seeing the first bi-value cell and the other seeing the second. Then y leaves every cell that sees both bi-value cells.
- Two non-peer cells with the same candidates {x,y}.
- A strong link on x connecting them (a conjugate pair).
- Eliminate y from cells that see both bi-value cells.
Worked example
- Two cells both show {4,7}.
- A column has 4 as a conjugate pair; one 4 sees the first cell, the other sees the second.
- If either {4,7} cell were 4, the strong link would force the other to be 7.
- So at least one of the two cells is 7.
- Remove 7 from any cell that sees both {4,7} cells.
Try it yourself
Tap a cell, then a number, to practise.
Frequently asked questions
- What is the "W" in W-Wing?
- It refers to the shape of the deduction path: two bi-value cells linked through a strong link, drawing a W-like zig-zag across the grid.
- How does it relate to coloring and chains?
- It is a short, named special case of an alternating inference chain — the same logic, packaged as an easy-to-spot pattern.
Related techniques
Practice: W-Wing
Put the W-Wing to work on a live board — free puzzles with notes, hints and four difficulty levels.
Try it on a live board