static L<S> ai_tripleRefsToTexts(S a, S b, S c, L<TripleRef<S>> l) {
  if (empty(l)) ret sharedEmptyList();
  new L<S> out;
  for (TripleRef<S> ref : l) if (ref != null) {
    T3<S> t = ref.triple;
    SS match = simpleMatchTriple_dollarVars(a, b, c, t);
    if (match != null)
      out.add(match.get("$X"));
    ifdef ai_tripleRefsToTexts_debug
    else
      print("No match: " + t);
    endifdef
  }
  ret out;
}