anchor.diff:  
   -include_lib("proper/include/proper.hrl").
   
  --export([initial_state/0, command/1, precondition/2, postcondition/3,
  -        next_state/3,request_stream/1,request_stream_with_size/2,
  -        append/2,simple_query/3,all_since/2,last_entry_at/2,
  -        timestamp/0,payload_to_list/2]).
  +-export([initial_state/0, command/1, precondition/2, postcondition/3, next_state/3]).
   
   -define(STREAMNAMES, [<<"tempfile">>, <<"file001">>, <<"anotherfile">>,
           <<"somefile">>, <<"binfile">>, <<"cakestream">>]).
  
positive.code:     case lists:keysearch(StreamName,1,S#state.streams) of
          {value, {StreamName,Data}} ->
              Expected = lists:sort([Y || {X,Y} <- Data, X>=Time]),
              Observed = lists:sort([Y || {X,Y} <- Result, X>=Start, X=<End]),
              Observed =:= Expected;
          false ->
              Result =:= []
  
negative.code:             case lists:keysearch(StreamName,1,S#state.streams) of
                  {value, {StreamName,Data}} ->
                      Expected = lists:sort([Y || {X,Y} <- Data, X>=Start, X=<End]),
                      Observed = lists:sort([Y || {_,Y} <- Result]),
                      Observed =:= Expected;
                  false ->
                      Result =:= []
  