interface i
{
  out void cb();

  behaviour
  {
    on optional: cb;
  }
}

interface ilivelock
{
  out void cb();

  behaviour
  {
    on inevitable: cb;
  }
}

component QueueFullExternal
{
  provides i p;
  requires external ilivelock r;

  behaviour
  {
    on r.cb(): {}
  }
}