anchor.diff:  
   handle_call({delete, Bucket, Before}, _From, State) ->
       {R, State1} = case get_set(Bucket, State) of
  -                      {ok, {{LastWritten, Res, MSet}, S1}} ->
  +                      {ok, {{LastWritten, MSet}, S1}} ->
                             {ok, MSet1} = mstore:delete(MSet, Before),
  -                          V = {LastWritten, Res, MSet1},
  +                          V = {LastWritten, MSet1},
                             MStore = gb_trees:enter(Bucket, V, S1#state.mstores),
                             {ok, S1#state{mstores = MStore}};
                         _ ->
  
positive.code: 
  handle_call({metrics, Bucket, Prefix}, _From, State) ->
      {MsR, State1} = case get_set(Bucket, State) of
                          {ok, {{_, _, M}, S2}} ->
                              Ms = mstore:metrics(M),
                              Ms1 = btrie:fetch_keys_similar(Prefix, Ms),
                              {btrie:from_list(Ms1), S2};
  
negative.code: %% @end
  %%--------------------------------------------------------------------
  terminate(_Reason, #state{mstores = MStore}) ->
      gb_trees:map(fun(_, {_, MSet}) ->
                           mstore:close(MSet)
                   end, MStore),
      ok.
  