anchor.diff:  
   start_link() ->
       gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
  -
  -possible_change() ->
  -    ?MODULE ! reset_ring_id.
   
   local_ensembles() ->
       Node = node(),
  
positive.code:     {noreply, State}.
  
  handle_info(tick, State) ->
      State2 = tick(State),
      schedule_tick(),
      {noreply, State2};
  
  handle_info(reset_ring_id, State) ->
      State2 = State#state{last_ring_id=undefined},
      {noreply, State2};
  
  handle_info(_Info, State) ->
      {noreply, State}.
  
negative.code: 
  init([]) ->
      schedule_tick(),
      {ok, #state{}}.
  
  handle_call(_Request, _From, State) ->
      {reply, ok, State}.
  