interface ihello
{
  in void hello();
  out void world();
  behaviour
  {
    bool idle = true;
    [idle] on hello: idle = !idle;
    [!idle] on hello: illegal;
    [!idle] on inevitable: {
      [true]{idle = !idle; world;}
      [true]{idle = !idle; world;}
    }
  }
}

component hello_inevitable_illegal
{
  provides ihello p;
  requires ihello r;

  behaviour
  {
    bool idle = true;
    [idle] on p.hello(): {idle = !idle; r.hello();}
    on r.world(): {idle = !idle; p.world();}
  }
}