trav->rtbst_node = trav->rtbst_node->rtbst_link[0];
while (trav->rtbst_node->rtbst_rtag == RTBST_CHILD)
  trav->rtbst_node = trav->rtbst_node->rtbst_link[1];
return trav->rtbst_node->rtbst_data;
