anchor.diff:  -spec subscribe(comm:mypid() | [comm:mypid()], cookie()) -> ok.
   subscribe([], _Cookie)         -> ok;
   subscribe(GlobalPids, Cookie) when is_list(GlobalPids) ->
  +    FD = my_fd_pid(),
       _ = [begin
  -             HBPid = get_hbs(Pid),
  -             comm:send_local(HBPid, {add_subscriber, self(), Pid, Cookie})
  +             comm:send_local(FD, {add_subscriber_via_fd, self(), Pid, Cookie})
            end
            || Pid <- GlobalPids],
       ok;
  
positive.code: -spec unsubscribe(comm:mypid() | [comm:mypid()], cookie()) -> ok.
  unsubscribe([], _Cookie)         -> ok;
  unsubscribe(GlobalPids, Cookie) when is_list(GlobalPids) ->
      _ = [begin
               HBPid = get_hbs(Pid),
               comm:send_local(HBPid, {del_subscriber, self(), Pid, Cookie})
           end
           || Pid <- GlobalPids],
      ok;
  
negative.code: on({pong, RemHBSSubscriber, RemoteDelay}, State) ->
      ?TRACE("FD: pong, ~p~n", [RemHBSSubscriber]),
      forward_to_hbs(RemHBSSubscriber, {pong_via_fd, RemHBSSubscriber, RemoteDelay}),
      State;
  
  on({add_subscriber_via_fd, Subscriber, WatchedPid, Cookie}, State) ->
      ?TRACE("FD: subscribe ~p to ~p (cookie: ~p)~n", [Subscriber, WatchedPid, Cookie]),
      forward_to_hbs(WatchedPid, {add_subscriber, Subscriber, WatchedPid, Cookie}),
      State;
  
  on({del_subscriber_via_fd, Subscriber, WatchedPid, Cookie}, State) ->
      ?TRACE("FD: unsubscribe ~p to ~p (cookie: ~p)~n", [Subscriber, WatchedPid, Cookie]),
      forward_to_hbs(WatchedPid, {del_subscriber, Subscriber, WatchedPid, Cookie}),
      State;
  
  on({add_watching_of_via_fd, Subscriber, Pid}, State) ->
  