GridWits
Expert tier Technique 16 of 21 Smart Hint: Skyscrapers and Skyscrapers+

W-Wing

Two cells share the same candidate pair and aren't in the same row or column, but a chain elsewhere forces one of them to one of those heights — eliminate the other height from any cell both see.

How it works

  1. 1Two cells far apart share the same candidate pair {1, 4}: the top-left corner and the middle.
  2. 2Now look at the bottom row. Height 4 fits in only two of its cells — one in the corner cell's column, one in the middle cell's column.
  3. 3One of those two IS the row's 4. Whichever it is, it knocks the 4 out of one of our pair, leaving that one as a 1.
  4. 4So at least one of the pair is a 1 — again, without knowing which.
  5. 5Any cell seeing both of them can't be 1. The two cells completing their rectangle each see one along a row and the other down a column: strike their 1s.
1 4 1 2 3 1 3 5 1 4 2 4 1 2 3 3 4 2 3 5 1 3 5
  • Height ruled out
  • Relationship — The arrow shows which cells support the deduction.
  • Conclusion — The final arrow lands beside the proved or ruled-out height.
Next in the ladder XYZ-Wing →

A three-candidate cell links to two two-candidate cells whose combined candidates match it exactly — the shared height can't be in any cell all three see.