interface ihello
{
  in void hello();

  behaviour
  {
    on hello: {}
  }
}

component helloworld
{
  provides ihello h;
  requires iworld w;

  behaviour
  {
    on h.hello(): w.world();
  }
}

interface iworld
{
  in void world();

  behaviour
  {
    on world: {}
  }
}

component hellosystem
{
  provides ihello h;
  requires iworld w;

  system
    {
      helloworld c;
      h <=> c.h;
      w <=> c.w;
    }
}