// A reachable transition t leading to an accepting places
// can be dead if unreachable transitions on the way block
// all firing sequences containing t.

PetriNet result = removeDead(removeUnreachable(n));

assert(numberOfTransitions(result) == 0);
assert(numberOfPlaces(result) == 0);
assert(isEmpty(result));

PetriNet n = (
  alphabet = {a b},
  places = {p1 p2 p3 p4},
  transitions = {
    ({p1} a {p2})
    ({p2 p3} b {p4}) 
  },
  initialMarking = {p1},
  acceptingPlaces = {p4}
);