GridWits
Medium tier Technique 14 of 31 Used by Smart Hint

Adjacent 3s

Two 3s side by side: the outer edge of each one — the side facing away from its partner — is always a line.

How it works

  1. 1Two 3s sharing an edge, with nothing else on the board. A 3 has exactly one blank side, so each cell is one X away from being fully drawn.
  2. 2Suppose the left 3's OUTER edge were that blank side. Then it takes its top, its bottom, and the edge it shares with its neighbour.
  3. 3The dot at the top of the shared edge now carries two lines — the left 3's top and the shared edge — so everything else there is blank, including the right 3's top. The dot at the bottom kills the right 3's bottom the same way, stranding it with only two usable sides.
  4. 4So the left 3's outer edge is a line, and by the mirror image so is the right 3's. Both are forced without ever deciding the shared edge, which really is still open here.
3 3
  • Edge the technique adds
  • Cells that establish the pattern
Next in the ladder 0 Beside a 3 →

A 0 next to a 3 settles the 3 outright: the shared edge is blank, so the 3's other three sides are all lines.