W-Wing

Level 8 · Blue Belt

Strategy:

Wings

Requires:

Naked Pair

Overview

W-Wing consists of two identical bi-value cells connected by a strong link on one of their candidates. The other candidate can be eliminated from cells that see both bi-value cells.

How It Works

  1. Find two bi-value cells with identical candidates {X,Y} that don't see each other.
  2. Find a strong link on digit X (or Y) connecting cells that each see one of the bi-value cells.
  3. If the strong link is on X, eliminate Y from cells that see both bi-value cells.

Example

Starting position

Look for W-Wing.

1

Matching bivalue cells r2c6 and r8c2

Find two bivalue cells with identical candidates: r2c6 and r8c2 both have { 5, 6 }.

2

A link on 5 joins the cells

These cells do not see each other, but a strong link on digit 5 connects them.

3

Strong link at r2c1-r9c1

The strong link is at r2c1-r9c1. If neither bivalue cell has 5, the link forces a contradiction.

4

One bivalue cell must be 6

Therefore, one of the bivalue cells must be 6. These cells that see both cannot keep 6: r8c6.

5

Remove 6 from common peers

Remove 6 from the cells that see both bivalue cells: r8c6.

6

Result

Result after applying the technique.

Tips & Patterns

  • W-Wings are relatively easy to spot once you know the pattern.
  • Look for matching bi-value cells first, then search for connecting strong links.
  • The elimination digit is the one NOT involved in the strong link.