static Pair<WebNode> web_bestNodeMatch(Web a, Web b) {
  new Best<Pair<WebNode>> best;
  
  for (WebNode n : web_nodes(a)) {
    new HashSet<WebNode> candidates;
    for (Lisp l : n.labels())
      candidates.addAll(b.index.get(l));
    for (WebNode c : candidates)
      best.put(pair(n, c), web_numberOfSharedLabels(n, c));
  }
  
  ret best!;
}