anchor.diff:  %%--------------------------------------------------------------------
   -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.
   
   
  
positive.code: 
  
  %%--------------------------------------------------------------------
  %% @doc append the new node(s) to the tree end.
  %%
  %%      NB: the add/2 call leaves the Tree in unindexed state.
  
negative.code: 
  %%--------------------------------------------------------------------
  %% @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
  