anchor.diff:  -spec(get_range/3 :: (db(), key(), key()) -> [{key(), value()}]).
   get_range(DB, From, To) ->
       F = fun ({Key, {Value, _, _, _}}, Data) ->
  -                case util:is_between(From, Key, To) andalso Value =/= empty_val of
  -                    true ->
  -                        [{Key, Value} | Data];
  -                    false ->
  -                        Data
  +                case Value =/= empty_val
  +                    andalso util:is_between(From, Key, To) of
  +                    true -> [{Key, Value} | Data];
  +                    false -> Data
                   end
           end,
       ?ETS:foldl(F, [], DB).
  
positive.code: %%      sized groups
  get_middle_key(DB) ->
      case (Length = ?ETS:info(DB, size)) < 3 of
          true ->
              failed;
          false ->
              {ok, nth_key(DB, Length div 2 - 1)}
      end.
  
  nth_key(DB, N) ->
  
negative.code:     Res = case ?ETS:lookup(DB, Key) of
                [{Key, {Value, _WriteLock, _ReadLock, Version}}] ->
                    {ok, Value, Version};
                [] -> {ok, empty_val, -1}
            end,
  %%     Stop = erlang:now(),
  %%     Span = timer:now_diff(Stop, Start),
  