anchor.diff:      %% unexpected
       {next_state, passive, S}.
   
  +passive({enqueue, Msg}, From, S = #state{}) ->
  +    gen_fsm:reply(From, ok),
  +    {next_state, passive, insert(Msg, S)}.
  +
   %% @private
   notify(active, S = #state{size=0}) ->
       {next_state, active, S};
  
positive.code: %% @doc Enqueues a message.
  -spec enqueue(pid(), term()) -> ok.
  enqueue(Queue, Msg) ->
      gen_fsm:send_event(Queue, {enqueue, Msg}).
  
  %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
  %%% gen_fsm Function Definitions %%%
  
negative.code: notify(_Msg, S = #state{}) ->
      %% unexpected
      {next_state, notify, S}.
  
  notify({enqueue, Msg}, From, S = #state{}) ->
      gen_fsm:reply(From, ok),
      send_notification(insert(Msg, S)).
  
  %% @private
  handle_event(_Event, StateName, State) ->
  