anchor.diff:  
   %% API
   -export([start_link/0,
  +         stop/0,
            reset/0,
            filter/2,
            collect/0, collect/1, collect/2,
  -         results/0]).
  +         results/0,
  +         stop_collect/0]).
   -export([test_all_events/1]).
   
   -export([all_events/1]).
  +-export([trigger_sentinel/0]).
   
   %% gen_server callbacks
   -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  
positive.code: 
  start_link() ->
      gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).
  
  reset() ->
      gen_server:call(?SERVER, reset).
  
negative.code:             {MinTs,_} = hd(STrace),
              R = zero_ts(MinTs, STrace, [])
      end,
      {reply, R, State};
  handle_call(stop, _From, State) ->
      {stop, normal, ok, State}.
  
  handle_cast(stop_sentinel, State) ->
      dbg:stop_clear(),
      case State#state.stop_from of
          undefined ->
              ok;
          StopFrom ->
              gen_server:reply(StopFrom, ok)
      end,
      {noreply, State#state{stop_from = undefined}};
  handle_cast(_Msg, State) ->
      {noreply, State}.
  
  handle_info(collect_timeout, State = #state{tracing = true}) ->
      handle_call(stop_collect, undefined, State);
  handle_info(collect_timeout, State) ->
      {noreply, State}.
  
  terminate(_Reason, _State) ->
  