anchor.diff:                                           AccIn
                                    end
                            end, [], DB),
  +    %% see HINT in foldl/3
       lists:foldr(Fun, Acc, Data).
   
   %% @doc foldr iterates over DB and applies Fun(Entry, AccIn) to every element
   %%      encountered in Interval. On the first call AccIn == Acc0. The iteration
   %%      stops as soon as MaxNum elements have been encountered.
  +%%      Returns a potentially larger-than-memory dataset. Use with care.
   -spec foldr(DB::db(), Fun::fun((Entry::entry(), AccIn::A) -> AccOut::A), Acc0::A,
                                  Intervall::db_backend_beh:interval(), MaxNum::non_neg_integer()) -> Acc1::A.
   foldr({DB, _FileName}, Fun, Acc, Interval, MaxNum) ->
  
positive.code:                                          AccIn
                                   end
                           end, [], DB),
      lists:foldl(Fun, Acc, Data).
  
  %% @doc foldl iterates over DB and applies Fun(Entry, AccIn) to every element
  %%      encountered in Interval. On the first call AccIn == Acc0. The iteration
  %%      stops as soon as MaxNum elements have been encountered.
  -spec foldl(DB::db(), Fun::fun((Entry::entry(), AccIn::A) -> AccOut::A), Acc0::A,
                                 Intervall::db_backend_beh:interval(), MaxNum::non_neg_integer()) -> Acc1::A.
  foldl({DB, _FileName}, Fun, Acc, Interval, MaxNum) ->
  
negative.code:                                       {Max, AccIn}
                                end
                        end, {MaxNum, []}, DB),
      %% see HINT in foldl/3
      lists:foldl(Fun, Acc, Data).
  
  %% @doc makes a foldr over the whole dataset.
  %%      Returns a potentially larger-than-memory dataset. Use with care.
  -spec foldr(DB::db(), Fun::fun((entry(), AccIn::A) -> AccOut::A), Acc0::A) -> Acc1::A.
  foldr({DB, _FileName}, Fun, Acc) ->
      Data = toke_drv:fold(fun(_Key, Entry, AccIn) ->
                                   [?OUT(Entry) | AccIn]
                           end, [], DB),
      %% see HINT in foldl/3
      lists:foldr(Fun, Acc, Data).
  
  %% @equiv foldr(DB, Fun, Acc0, Interval, get_load(DB))
  %% @doc   Returns a potentially larger-than-memory dataset. Use with care.
  -spec foldr(DB::db(), Fun::fun((entry(), AccIn::A) -> AccOut::A), Acc0::A,
                                 Interval::db_backend_beh:interval()) -> Acc1::A.
  foldr({DB, _FileName}, Fun, Acc, Interval) ->
  