interface I {
  in void e();
  out void ec();

  behaviour {
    enum State { idle, busy };
    State s = State.idle;
    [s.idle] {
      on e: s = State.busy;
    }
    [s.busy] {
      on e: illegal;
      on inevitable: { ec; s = State.idle;}
    }
  }
}

interface II {
  in void e();
  out void ec();

  behaviour {
    enum State { idle };
    State s = State.idle;
    [s.idle] {
      on e: ec;
    }
  }
}

component external_asynchronous_sync_illegal {
  provides I p;
  requires II r;

  behaviour {
    enum State { idle, busy };
    State s = State.idle;
    [s.idle] {
      on p.e(): { r.e(); s = State.busy; }
      on r.ec: illegal;
    }
    [s.busy] {
      on p.e: illegal;
      on r.ec(): { p.ec(); s = State.idle;}
    }
  }
}