static S ai_matrixGet(S topic, S category) {
  new LinkedHashSet<S> v;
  new LinkedHashSet<S> u;
  if (has_verified(topic, "is", category)) v.add("yes");
  if (has_verified(topic, "is not", category)) v.add("no");
  if (has(topic, "is", category)) u.add("yes");
  if (has(topic, "is not", category)) u.add("no");
  
  v.addAll(ai_matrixUnpack(ai_texts_verified(topic, "$X", category)));
  u.addAll(ai_matrixUnpack(ai_texts(topic, "$X", category)));
  
  u.removeAll(v);
  new L<S> l;
  if (nempty(v)) l.add(joinWithComma(v));
  if (nempty(u)) l.add("unverified: " + joinWithComma(u));
  ret join(". ", l);
}