This problem has a deep connection to formal methods: one of the first formal models of concurrent computing was Petri nets, which are equivalent to VASes. Petri nets are very limited in what they can model, and so finding reachability even those tiny, limited programs is HACK-complete!
What I love so much about this is that it's really hard to find intuitive examples of TOWER-complete or even 2-EXPTIME-complete programs, but this one is so much harder than all of them but can easily be explained to a fifth-grader.
Next goal is to find an intuitive HYPERACK problem...
What I love so much about this is that it's really hard to find intuitive examples of TOWER-complete or even 2-EXPTIME-complete programs, but this one is so much harder than all of them but can easily be explained to a fifth-grader.
Next goal is to find an intuitive HYPERACK problem...