interface ihello {
  in void hello();
  in void cancel();
  out void world();
  behaviour {
    bool triggered = false;

    [!triggered] on hello: triggered = true;
    [triggered] on hello: illegal;

    on cancel: triggered = false;
    [triggered] on inevitable: {
      world;
      triggered = false;
    }
  }
}

component hello_external {
  provides ihello h;
  requires external ihello w;

  behaviour {
    bool triggered = false;
    [!triggered] on h.hello(): {
      w.hello();
      triggered = true;
    }
    on h.cancel(): {
      w.cancel();
      triggered = false;
    }
    [triggered] on w.world(): {
      h.world();
      triggered = false;
    }
  }
}