anchor.diff:  %% @doc Clear the specified index_hashtree, clearing all associated hashtrees
   clear(Tree) ->
       gen_server:call(Tree, clear, infinity).
  +
  +%% @doc Expire the specified index_hashtree
  +expire(Tree) ->
  +    gen_server:call(Tree, expire, infinity).
   
   %%%===================================================================
   %%% gen_server callbacks
  
positive.code:     hashtree:write_meta(<<"built">>, <<1>>, Tree0),
      hashtree:write_meta(<<"build_time">>, term_to_binary(BuildTime), Tree0),
      riak_kv_entropy_info:tree_built(Index, BuildTime),
      State#state{built=true, build_time=BuildTime}.
  
  %% Determine the build time for all trees associated with this
  %% index. The build time is stored as metadata in the on-disk file. If
  
negative.code:     State2 = lists:foldl(fun(Id, StateAcc) ->
                                   do_new_tree(Id, StateAcc)
                           end, State, IndexNs),
      State2#state{built=false, expired=false}.
  
  -spec load_built(state()) -> boolean().
  load_built(#state{trees=Trees}) ->
  