TODO: check; improve
Things that aren't going well:
- On the example graph BRP-16-2, all nodes have distance 1. I that
possible??
- The initial states list themself as their own predecessor. That's
bad, because it's simply false (unless there is a self-loop).
Former-commit-id: 06f9a28306 [formerly e7e2385e0d]
Former-commit-id: 3505011831