anchor.diff:  -spec foldl(DB::db(), Fun::fun((Entry::entry(), AccIn::A) -> AccOut::A), Acc0::A,
                                  Intervall::backend_beh:interval(), MaxNum::non_neg_integer()) -> Acc1::A.
   foldl({DB, _FileName}, Fun, Acc, Interval, MaxNum) ->
  -    {_Left, Data} = toke_drv:fold(fun(_Key, Entry, {Max, AccIn}) ->
  -                                 DeCoded = ?OUT(Entry),
  -                                 case is_in(Interval, element(1, DeCoded))
  -                                      andalso Max > 0 of
  -                                     true ->
  -                                         {Max - 1, [DeCoded | AccIn]};
  -                                     _ ->
  -                                         {Max, AccIn}
  -                                 end
  -                         end, {MaxNum, []}, DB),
  +    {_Left, Data} = toke_drv:fold(
  +                      fun(_Key, _Entry, {0, _} = AccIn) ->
  +                              AccIn;
  +                         (_Key, Entry, {Max, AccIn}) ->
  +                              DeCoded = ?OUT(Entry),
  +                              case is_in(Interval, element(1, DeCoded)) of
  +                                  true ->
  +                                      {Max - 1, [DeCoded | AccIn]};
  +                                  _ ->
  +                                      {Max, AccIn}
  +                              end
  +                      end, {MaxNum, []}, DB),
       lists:foldl(Fun, Acc, Data).
   
   %% @doc Is equivalent to ets:foldr(Fun, Acc0, DB).
  
positive.code: %% @doc Deletes the tuple saved under Key and returns the new DB.
  %%      If such a tuple does not exists nothing is changed.
  -spec delete(DB::db(), Key::key()) -> db().
  delete({DB, FileName}, Key) ->
      toke_drv:delete(DB, ?IN(Key)),
      {DB, FileName}.
  
  %% @doc Returns the name of the DB specified in new/1.
  -spec get_name(DB::db()) -> nonempty_string().
  
negative.code: %% @doc Saves arbitrary tuple Entry in DB DBName and returns the new DB.
  %%      The key is expected to be the first element of Entry.
  -spec put(DB::db(), Entry::entry()) -> db().
  put({DB, _FileName} = State, Entry) ->
      toke_drv:insert(DB, ?IN(element(1, Entry)), ?IN(Entry)),
      State.
  
  %% @doc Returns the entry that corresponds to Key or {} if no such tuple exists.
  -spec get(DB::db(), Key::key()) -> entry() | {}.
  