anchor.diff:              comm:send(Pid, {get_trace_reply, lists:reverse(Msgs)})
       end,
       State;
  -on({clear_trace, TraceId}, State) ->
  -    lists:keytake(TraceId, 1, State).
  +on({cleanup, TraceId}, State) ->
  +    case lists:keytake(TraceId, 1, State) of
  +        {value, _Tuple, TupleList2} -> TupleList2;
  +        false                       -> State
  +    end.
   
   passed_state_new(TraceId, Logger) -> {TraceId, Logger}.
   passed_state_trace_id(State)      -> element(1, State).
  
positive.code: 
  %% client functions
  -export([start/0, start/1, start/2, stop/0]).
  -export([get_trace/0, get_trace/1, cleanup/1]).
  
  %% trace analysis
  -export([send_histogram/1]).
  
negative.code:     receive
          ?SCALARIS_RECV({get_trace_reply, Log}, Log)
      end.
  
  -spec cleanup() -> ok.
  cleanup() -> cleanup(default).
  
  -spec cleanup(trace_id()) -> ok.
  cleanup(TraceId) ->
  