anchor.diff:  handle_call({trace, Type, Message}, _From, #state{trace=Trace0}=State) ->
       %% lager:info("~p: recording trace type: ~p message: ~p", [?MODULE, Type, Message]),
       {reply, ok, State#state{trace=Trace0++[{Type, Message}]}};
  -handle_call({replay, Type, Message}, From, #state{previous_trace=PreviousTrace0, replay=Replay, blocked_processes=BlockedProcesses0}=State) ->
  +handle_call({replay, Type, Message}, From, #state{previous_trace=PreviousTrace0, replay=Replay, shrinking=Shrinking, blocked_processes=BlockedProcesses0}=State) ->
       case Replay of 
           true ->
               %% Find next message that should arrive based on the trace.
               %% Can we process immediately?
  -            case can_deliver_based_on_trace({Type, Message}, PreviousTrace0, BlockedProcesses0) of 
  +            case can_deliver_based_on_trace(Shrinking, {Type, Message}, PreviousTrace0, BlockedProcesses0) of 
                   true ->
                       %% Deliver as much as we can.
  -                    {PreviousTrace, BlockedProcesses} = trace_deliver(PreviousTrace0, BlockedProcesses0),
  +                    {PreviousTrace, BlockedProcesses} = trace_deliver(Shrinking, {Type, Message}, PreviousTrace0, BlockedProcesses0),
   
                       %% Record new trace position and new list of blocked processes.
                       {reply, ok, State#state{blocked_processes=BlockedProcesses, previous_trace=PreviousTrace}};
  
positive.code: -record(state, {previous_trace=[],
                  trace=[], 
                  replay=false,
                  blocked_processes=[],
                  identifier=undefined}).
  
  
negative.code: 
              lager:info("~p: trace loaded.", [?MODULE]),
  
              Shrinking = case os:getenv("SHRINKING") of 
                  false ->
                      false;
                  _ ->
                      true
              end,
  
              #state{trace=[], previous_trace=Lines, replay=true, shrinking=Shrinking, blocked_processes=[], identifier=undefined}
      end.
  
  %% @private
  