anchor.diff:  
   get_written_interval(L) ->
       ?LET({O, Ln}, elements(L), {O+1, Ln-1}).
  - 
  +
   %% INITIALIZATION
   
   -record(state, {pid, prev_extra = 0,
  +                filename = undefined,
                   planned_writes=[],
                   planned_trims=[],
                   written=[],
                   trimmed=[]}).
   
  -initial_state() -> #state{written=[{0,1024}]}.
  -initial_state(I, T) -> #state{written=[{0,1024}],
  -                              planned_writes=I,
  -                              planned_trims=T}.
  +-define(FILENAME, "machi_file_proxy_eqc_data").
  +
  +initial_state() ->
  +    %%#state{filename=undefined, written=[{0,1024}]}.
  +    {_, _, MS} = os:timestamp(),
  +    Filename = test_server:temp_name("eqc_data") ++ "." ++ integer_to_list(MS),
  +    %% Filename = ?FILENAME,
  +    #state{filename=Filename, written=[{0,1024}]}.
  +
  +initial_state(I, T) ->
  +    S=initial_state(),
  +    S#state{written=[{0,1024}],
  +            planned_writes=I,
  +            planned_trims=T}.
   
   weight(_S, rewrite) -> 1;
   weight(_S, _) -> 2.
  
positive.code:     S1#state{prev_extra=0,
               planned_trims=tl(S#state.planned_trims)}.
  
  %% Property
  
  prop_ok() ->
    cleanup(),
    ?FORALL({I, T},
            {shuffle_interval(), shuffle_interval()},
      ?FORALL(Cmds, parallel_commands(?MODULE, initial_state(I, T)),
      begin
          {H, S, Res} = run_parallel_commands(?MODULE, Cmds),
          %% case S#state.pid of
          %%     undefined -> noop;
          %%     Pid ->
          %%         machi_file_proxy:stop(Pid)
          %% end,
          pretty_commands(?MODULE, Cmds, {H, S, Res},
                          aggregate(command_names(Cmds), Res == ok))
      end)
    ).
  
  %% Test for tester functions
  chopper_test_() ->
  
negative.code: %% append
  
  append_pre(S) ->
      S#state.pid /= undefined.
  
  %% do not allow appends with empty binary data
  