anchor.diff:  
   %%--------------------------------------------------------------------
   %% @doc return true if Tree is ready for queries, false otherwise.
  +%%
   %%    If this function returns false it means the Tree needs to be
   %%    reindexed, for example, after the call to add/2 or the process
   %%    of reindexing is currently ongoing in background and we need to
  
positive.code: %%--------------------------------------------------------------------
  -spec insert(tref(), [tnode()] | tnode()) -> ok | {error, Reason::term()}.
  insert(_Tree, _Points) ->
      ?not_loaded.
  
  %%--------------------------------------------------------------------
  %% @private
  %% @doc compare given trees for equality
  %% @end
  %%--------------------------------------------------------------------
  -spec compare(tref(), tref()) -> equal | diff.
  compare(_Tree1, _Tree2) ->
      ?not_loaded.
  
  
  
negative.code:     ?not_loaded.
  
  %%--------------------------------------------------------------------
  %% @doc export the Tree object into erlang Term
  %% @end
  %%--------------------------------------------------------------------
  -spec gettree(tref()) -> {ok, Term::[tnode()]} | {error, Reason::term()}.
  