GridWits
Expert tier Technique 13 of 46 Used by Smart Hint

W-Wing

Two cells with the same candidate pair, linked by a strong chain on one digit elsewhere on the board.

How it works

  1. 1A1 and I7 both carry the same candidate pair {4, 7}, but they don't share a row, column, or box, so they can't rule each other out directly.
  2. 2Column E has a strong link on 4: E1 and E7 are the only two candidates for 4 in that column, and each sits in the same row as one of the bivalue cells.
  3. 3If E1 is the 4 then A1 can't be, so A1 is 7; if E7 is the 4 then I7 is 7. Either way at least one of A1 and I7 holds a 7.
  4. 4I1 sees both — A1 across row 1, I7 down column I — so 7 can be eliminated there.

Play a Sudoku that needs this technique →

A 1 B 2 C 3 D 4 E 5 F 6 G 7 H 8 I 9 4 7 4 9 5 7 2 4 4 7 4 7 4 4 4 7 7
  • First colour in the chain
  • Cells that establish the pattern
  • Where the conclusion lands
  • Candidate ruled out
Next in the ladder XYZ-Wing →

Like XY-Wing, but the pivot keeps a third candidate, which tightens where the elimination applies.