anchor.diff:  is_in({element, Key}, OtherKey) -> Key ?EQ OtherKey;
   is_in(all, _Key) -> true;
   is_in({interval, '(', L, R, ')'}, Key) -> Key > L andalso Key < R;
  -is_in({interval, '(', L, R, ']'}, Key) -> Key > L andalso ((Key < R) or (Key ?EQ R));
  -is_in({interval, '[', L, R, ')'}, Key) -> ((Key > L) or (Key ?EQ L)) andalso Key < R;
  -is_in({interval, '[', L, R, ']'}, Key) -> ((Key > L) or (Key ?EQ L)) andalso ((Key < R) or (Key ?EQ R)).
  +is_in({interval, '(', L, R, ']'}, Key) -> Key > L andalso ((Key < R) orelse (Key ?EQ R));
  +is_in({interval, '[', L, R, ')'}, Key) -> ((Key > L) orelse (Key ?EQ L)) andalso Key < R;
  +is_in({interval, '[', L, R, ']'}, Key) -> ((Key > L) orelse (Key ?EQ L)) andalso ((Key < R) orelse (Key ?EQ R)).
  
positive.code: -spec prop_foldl([backend_beh:entry()], backend_beh:interval(),
                   non_neg_integer()) -> true.
  prop_foldl(Data, Interval, MaxNum) ->
      {DB1, ScrubedData} =
                           write_scrubed_to_db(?TEST_DB:new(randoms:getRandomString()),
                                               Data),
      {ExpInInterval, _NotIn} = lists:partition(
                                  fun(E) ->
                                          is_in(Interval, element(1, E))
                                  end,
                                  ScrubedData),
      ExpInIntervalCounted = lists:sublist(lists:keysort(1, ExpInInterval), MaxNum),
      AllFold = ?TEST_DB:foldl(DB1, fun(E, AccIn) -> [E | AccIn] end, []),
      IntervalFold = ?TEST_DB:foldl(DB1,
  
negative.code:                             MaxNum),
      %% ct:pal("ExpInInterval: ~p~nIntervalFold: ~p~nInterval: ~p~n", [ExpInInterval,
      %%                                                  IntervalFold, Interval]),
      ?equals_w_note(lists:sort(ScrubbedData), lists:sort(AllFold), "test_foldr1"),
      ?equals_w_note(lists:sort(ExpInInterval), lists:sort(IntervalFold), "test_foldr2"),
      ?equals_w_note(lists:sort(ExpInIntervalCounted),
                     lists:sort(IntervalCountFold), "test_foldr3"),
  