static Web web_mergeWebs(Web web1, Web web2) {
  Web web = web_cloneWeb(web1);
  web_addWebToWeb(web2, web);
  web_mergeNodesByFirstLabel(web);
  ret web;
}

static Web web_mergeWebs(Collection<Web> webs) {
  if (empty(webs)) null;
  Iterator<Web> i = webs.iterator();
  Web web = web_cloneWeb(i.next());
  while (i.hasNext())
    web_addWebToWeb(i.next(), web);
  web_mergeNodesByFirstLabel(web);
  ret web;
}