static void ai_spec_checkFact(S question) {
  for (S fact : ai_texts(question, "asks about fact:", "$X")) {
    if (ai_hasTriple_vary(fact, "is", "never a certain fact"))
      ai_postTriple("You can never be sure about that", "answers", question);
    if (ai_hasTriple_vary(fact, "is", "probably not true"))
      ai_postTriple("Probably not", "answers", question);
  }
}