W-Wing
Prerequisites: XY-Wing, Skyscraper
Overview
A W-Wing joins two cells with the same two candidates through a strong link on one of those digits. It proves that at least one of the two cells holds the other digit, so that digit can go from every cell that sees both.
How It Works
Find two bivalue cells sharing the same pair (A,B) that don't see each other. Find a strong link on digit A — a house where A appears in exactly two cells, one visible to each bivalue cell. The chain forces: if one bivalue cell = A, the strong link fires and the other bivalue cell must be B. If one bivalue cell = B, it already holds B. Either way, B is guaranteed in at least one bivalue cell — so eliminate B from all cells that see both.
When To Use It
Look for W-Wings when you find two bivalue cells with identical candidates that don't share a row, column, or box. Search for a strong link on one of their digits that bridges between them.
How To Detect It
Find pairs of bivalue cells with the same two candidates that don't see each other. For each shared digit, find a strong link (unit with that digit in exactly two cells) where one end sees each bivalue cell. Eliminate the other digit from cells seeing both bivalue cells.
Visual Example
Step 1 of 9
Two Matching Cells and a Bridge
A W-Wing uses two cells with the same two candidates that don't see each other, plus a strong link on one of those digits. Together they prove that one of the two cells holds the other digit.
Candidates already ruled out by earlier techniques aren't shown.
Practice
Your goal: fill the highlighted cell. Select a cell, then pick a number.
A W-Wing is hiding here. Find the two matching cells and their bridge, then eliminate and fill the Naked Single.Candidates already ruled out by earlier techniques aren't shown.
Use it in a real game
Hard puzzles are where you'll need techniques like this one.
Play a Hard puzzle