sbool ai_tripleToTripleRef_debug;

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