Peak Sudoku
Fish, wings, chains & uniquenessPeak Score 65–80

W-Wing

Two bivalue cells with identical candidates, bridged by a strong link on one digit.

Also known as: W-Wing Dual Bivalue

Quick Summary

Two identical bivalue cells connected by a strong link on one of their digits ensure at least one bivalue cell must take the other digit, eliminating it from cells seeing both.

Understanding the W-Wing Technique

A W-Wing combines two identical bivalue cells (for example, both holding 3 and 8) that do not see each other, bridged by an external strong link on digit 8. If digit 8 can only go in two cells of some row, column, or box, and those two cells each see one of the 3/8 cells, it is impossible for both cells to take 8. Therefore, at least one of them must take 3, eliminating candidate 3 from any cell in the grid that sees both bivalue cells.

Visual Examples

Green cells highlight the W-Wing pattern, amber cells denote where candidates are affected, and struck-through pencil marks show the eliminations. Use the buttons or arrow keys to browse examples.

Example 1 of 5
R5C6 and R9C5 both hold only {3,9}, and in row 2 the digit 3 links them. Either way one of the two ends up 9, so any cell that sees both can't be 9.
Removes: 9 from R4C5, R6C5, R9C6

How to Spot & Solve a W-Wing (Step-by-Step Guide)

The complete visual scanning and logical deduction process to execute this technique:

  • 1Find two separated cells with the exact same two candidates (for example, both holding 3 and 8).
  • 2Look for a strong link on digit 8 somewhere on the board (a row, column, or box where 8 only fits in two spots).
  • 3Check that one end of this strong link sees the first cell, and the other end sees the second cell.
  • 4Since one end of the bridge must be 8, it is impossible for both 3/8 cells to take 8.
  • 5Therefore, at least one of the two cells must take 3.
  • 6Eliminate candidate 3 from any cell that sees both of the original cells.

Common Traps & Mistakes to Avoid

  • Connecting the strong link on the same digit you are trying to eliminate.
  • Failing to confirm that S1 and S2 form a genuine strong link (exactly two occurrences in that house).
  • Eliminating from cells that do not see BOTH bivalue cells.

Frequently Asked Questions

What is a strong link in Sudoku?

A strong link means a relationship where if one candidate is false, the other MUST be true. For example, if digit 5 appears in only two cells of a row, those two cells have a strong link on 5.

Expand your repertoire by learning prerequisites and advanced counterparts:

XY-WingPeak Score 55–70

Three bivalue cells – a hinge and two pincers.

Read guide →
XY-ChainPeak Score 70–85

A chain of bivalue cells that forces a digit at both endpoints.

Read guide →
SkyscraperPeak Score 60–75

Two rows (or columns) where a digit has exactly two positions, sharing one column (or row).

Read guide →

Ready to Practice W-Wing?

Try a puzzle in the Tough tier (Peak Score 61–70), or browse all 25 techniques.

Play Tough puzzleAll 25 techniques