anchor.diff:  %%      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)}
  +        true -> failed;
  +        false -> {ok, nth_key(DB, Length div 2 - 1)}
       end.
   
   nth_key(DB, N) ->
  
positive.code:                             ReadLock == 0 andalso
                              OldVersion < Version of
                              true ->
                                  ?ETS:insert(DB, {Key, {Value, WriteLock, ReadLock, Version}}), 
                                  DB;
                              false ->
                                  DB
                          end
                  end
          end,
  
negative.code:             {DB, ok};
          [{Key, {_Value, false, _ReadLock, _Version}}] ->
              {DB, failed};
          [] -> {DB, failed}
      end.
  
  %% @doc sets a read lock on a key
  