Highlander
Uses the fact that the puzzle has exactly ONE solution: any move that would leave two different valid answers must be wrong. Powerful, but it's reasoning about the puzzle rather than about the loop.
The solver does not attempt this technique, so Smart Hint will never suggest it. It is documented because you may still want to spot it yourself.
How it works
- 1This board is stuck: not one technique in this guide moves on it from a blank start, yet it has exactly one solution, which is the only situation where the argument below is worth reaching for.
- 2You are allowed to use the promise of uniqueness. Look for a small patch where two different arrangements would both satisfy every clue touching it and would look identical from outside — same edges crossing the patch's border, same everything.
- 3If such a pair really could both occur you would have two valid answers, and the puzzle says there is one. So whatever move would leave both arrangements open is the wrong move.
- 4A 2 with no clued neighbours is the classic seed, because its two ways of turning are so often interchangeable from outside.
- 5Treat it as a last resort: it tells you nothing about WHY the loop goes that way, and it is the one technique that stops working the moment a puzzle has a second solution by mistake.
- Cells that establish the pattern