GridWits
Extreme tier Technique 28 of 31 Used by Smart Hint

Extra Long Dead End

Follow a candidate through more than fifteen forced continuations. If that extended chain eventually leaves the line with no exit, the original candidate is ruled out.

How it works

  1. 1Suppose the first highlighted edge is a line, then follow only forced clue-count and dot-rule consequences.
  2. 2The line keeps travelling: seventeen forced continuations are needed before anything fails. That is more than the fifteen-continuation boundary for an Extra Long Dead End.
  3. 3At the end of the highlighted route, one line reaches a dot whose other exits are all crossed off. The loop cannot stop there.
  4. 4So the original supposition was wrong: cross off the first highlighted edge. The unusually long trace makes this Extreme work.
1 3 1 3 2 2 1 0 1 3
  • Edge on the loop
  • Edge ruled out
  • Cells that establish the pattern
Next in the ladder Connectivity →

The finished loop is a single connected shape, so every line already drawn has to end up joined to every other one. An edge marooned in a pocket the drawn lines can never reach is ruled out.