anchor.diff:  -record(state, {version       :: integer(),
                   ensemble_data :: ensembles(),
                   remote_peers  :: orddict(peer_id(), pid()),
  -                cluster_state :: cluster_state(),
  -                subscribers :: [fun()]
  +                cluster_state :: cluster_state()
                  }).
   
   -type state() :: #state{}.
  
positive.code:             {noreply, State}
      end;
  
  handle_call({subscribe, Callback}, _, State=#state{subscribers=Subscribers}) ->
      %% TODO: Change subscriber API to prevent multiple subscriptions with the same callback.
      Subscribers2 = [Callback|Subscribers],
      application:set_env(riak_ensemble, subscribers, Subscribers2),
      State2 = State#state{subscribers=Subscribers2},
      {reply, ok, State2};
  
  handle_call(_Request, _From, State) ->
      {reply, ok, State}.
  
  
negative.code:          remove/2,
           enabled/0,
           enable/0,
           create_ensemble/4,
           create_ensemble/5,
           known_ensembles/0,
  