static S ai_sr_patternize(S s) {
  L<S> tok = ai_someSplit(s);
  for (int i = 1; i < l(tok); i += 2) {
    S category = ai_text(tok.get(i), "is", "$X");
    if (category != null)
      tok.set(i, "<" + category + ">");
  }
  ret join(tok);
}