static TripleRef<S> ai_tripleToTripleRef(TripleWeb w, S searchTerm, int occurrence) {
  if (w == null) null;
  // occurrence count magic
  for (int i = 0; i < 3; i++)
    if (eqic(tripleGet(w, i), searchTerm)) {
      if (occurrence-- == 0) ret tripleRef(w, i);
    }
  null;
}