anchor.diff:  -export([foldl/3, foldl/4, foldl/5]).
   -export([foldr/3, foldr/4, foldr/5]).
   
  --type db() :: tid() | atom().
  +-type db() :: ets:tab().
   -type key() :: db_backend_beh:key(). %% '$end_of_table' is not allowed as key() or else iterations won't work!
   -type entry() :: db_backend_beh:entry().
   
  
positive.code: foldr(_DB, _Fun, Acc, {interval, _, _End, '$end_of_table', _}, _MaxNum) -> Acc;
  foldr(_DB, _Fun, Acc, {interval, _, '$end_of_table', _Start, _}, _MaxNum) -> Acc;
  foldr(_DB, _Fun, Acc, {interval, _, End, Start, _}, _MaxNum) when Start < End -> Acc;
  foldr(DB, Fun, Acc, {element, El}, _MaxNum) -> 
      case ets:lookup(DB, El) of
          [] ->
              Acc;
  
negative.code: foldl(_DB, _Fun, Acc, {interval, _, '$end_of_table', _End, _}, _MaxNum) -> Acc;
  foldl(_DB, _Fun, Acc, {interval, _, _Start, '$end_of_table', _}, _MaxNum) -> Acc;
  foldl(_DB, _Fun, Acc, {interval, _, Start, End, _}, _MaxNum) when Start > End -> Acc;
  foldl(DB, Fun, Acc, {element, El}, _MaxNum) ->
      case ets:lookup(DB, El) of
          [] ->
              Acc;
  