static LL<S> ai_splitCompoundWord2(S s) {
  new LL<S> out;
  for (int i = 1; i < l(s)-1; i++) {
    S a = substring(s, 0, i), b;
    if (ai_isWord(a) && ai_isWord(b = substring(s, i)))
      out.add(ll(a, b));
  }
  ret out;
}