static L<S> ai_getRelation(S a, S b) {
  new LinkedHashSet<S> relations;
  for (WebNode n : indexedNodes(a)) {
    L<WebRelation> rels = web_relationsToNodeNamed(n, b);
    for (WebRelation r : rels)
      relations.addAll(web_texts(r));
  }
  ret relations;
}