[Coda]

If you can solve it without a guess, it follows that the solution is unique. The converse does not hold; a unique solution may still require guessing.

I have no desire to ensure that a puzzle can be solved without guessing. I've solved plenty of puzzles that require guessing. They're harder, to be sure, but I consider that a feature. (It WOULD be nice to heuristically guess at a puzzle's difficulty, though.)

Only once have I managed to get into a state where all of the runs are satisfied but I didn't have the accepted solution. It's possible that other puzzles I've solved in the past could have had similar faux solutions; it's not something I've paid attention to.

EDIT: Ack! Now it's twice, and this time I can't figure out what the other solution is... Okay, this might be more important than I thought. 15x15 seed 842082313.

EDIT 2: Never mind, it was a bug in the board validation. The solution on this one is unique.