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