static void webs_toTripleFile(L<Web> webs, PrintWriter out) {
  new L<S> names;
  new Map<S, Int> index;
  new StringBuilder buf;
  for (Web web : webs) {
    T3<S> t = ai_webToTriple(web);
    if (t == null) fail("Not tripelizable: " + webToStringShort(web));
    buf.append(
      webs_toTripleFile_indexGet(names, index, t.a) + " " +
      webs_toTripleFile_indexGet(names, index, t.b) + " " +
      webs_toTripleFile_indexGet(names, index, t.c) + "\n");
  }
  out.println(struct(names));
  out.print(buf);
}