anchor.diff:          [{Key, {_Value, WriteLock, ReadLock, _Version}}] ->
               % better use ets:update_element?
               ?ETS:insert(DB, {Key, {Value, WriteLock, ReadLock, Version}});
  -        [] ->
  -            ?ETS:insert(DB, {Key, {Value, false, 0, Version}})
  +        [] -> ?ETS:insert(DB, {Key, {Value, false, 0, Version}})
       end,
       DB.
   
  
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: %%      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) ->
  