static S ai_varyClassification(L<S> l) {
  if (l(l) <= 1) ret null;
  S original = unquote(last(l));
  for (S category : dropLast(l)) {
    try answer random(listWithoutIC(ai_texts("$X", "is a subclass of", category), original));
    try answer random(listWithoutIC(ai_texts("$X", "is a", category), original));
  }
  null;
}