interface ihello
{
  in void hello();

  behaviour
  {
    on hello: {}
  }
}

component helloguard
{
  provides ihello h;
  requires iworld w;

  behaviour
  {
    bool b = false;
    on h.hello():
      {
        [b] {b=!b;w.cruel ();}
        [!b] {b=!b;w.world ();}
      }
  }
}

interface iworld
{
  in void cruel();
  in void world();

  behaviour
  {
    on cruel: {}
    on world: {}
  }
}