Technique

W-Wing

Two cells, anywhere on the board, that share the exact same two candidates {X,Y}, linked by a chain where X can only be one of two places. That link forces one of the two cells to be Y.

💡 What It Is

A pattern connecting two bivalue cells with identical candidates through a 'strong link' - a pair of cells elsewhere where a digit must be in one or the other.

🔍 How To Spot It

Find two bivalue cells with the same candidates {X,Y}. Look for a strong link on X - a row, column, or box where X can only go in two cells - with one end seeing one of the bivalue cells and the other end seeing the other.

✅ Why It Works

If the first bivalue cell isn't Y, it's X - which pushes the strong link's other end to not-X, forcing it toward Y territory, which in turn forces the second bivalue cell away from Y... the logic ping-pongs until at least one of the two bivalue cells is proven to be Y. Since one of them always is, Y can be eliminated from any cell that sees both.

📝 Worked Example

R1C2 and R8C2 both have candidates {4,6}. Digit 6 forms a strong link between R1C7 and R8C7 in column 7 (i.e. within column 7, 6 can only go in one of those two cells). R1C2 sees R1C7 and R8C2 sees R8C7, closing the loop - eliminate 4 from any cell that sees both R1C2 and R8C2.

Ready to try it yourself?

Practice this →