The W-Wing Technique in Sudoku
The W-Wing is a neat two-cell pattern that often hides in plain sight. Two cells share the same pair of candidates {X, Y}, and a strong link on one digit between them forces the other digit out of any cell that sees both.
How to use the W-Wing, step by step
- Find two cells, not seeing each other, with the same two candidates {X, Y}.
- Look for a unit where one of those digits — say X — has only two spots, each seeing one of the two cells (a strong link on X).
- That strong link means the two cells cannot both be X, so one of them must be Y.
- Find cells that see both {X, Y} cells.
- Eliminate Y from those cells, since one of the pair is always Y.
- Re-scan for new singles.
What is a W-Wing?
A W-Wing is two bi-value cells with identical candidates {X, Y}, connected by a strong link on X in some unit between them. The strong link guarantees the two cells are not both X, so at least one is Y — and any cell seeing both can lose Y. It is a close relative of the Y-Wing, using a conjugate pair as the bridge instead of a pivot.
How to spot a W-Wing
Look for matching bi-value pairs first, then check whether a single digit links them with a strong link (a row, column or box where that digit has just two candidates). If it does, the other digit is your elimination target. Keep candidates tidy and consult tips & strategy for the surrounding techniques.
W-Wing in Sudoku: FAQ
What is a W-Wing in Sudoku?
A W-Wing is two cells with the same two candidates {X, Y} joined by a strong link on one of those digits. The link forces at least one of the cells to be the other digit, so any cell seeing both can have that digit removed.
How is a W-Wing different from a Y-Wing?
A Y-Wing uses a pivot cell and two different pincers sharing a third digit. A W-Wing uses two cells with identical candidates bridged by a strong link on one digit. Both end in eliminating a shared digit from common peers.
When should you use a W-Wing?
It is a hard-grid technique, used after singles and pairs stall. Because it only needs two matching bi-value cells and a strong link, it is often quicker to spot than the longer chains.