public static Stella_Object prognify(Cons trees) {
    switch (trees.length()) {
      case 0: 
        return (Stella.NIL);
      case 1: 
        { Stella_Object tree = trees.value;

          trees.firstSetter(null);
          return (tree);
        }
      default:
        return (Cons.cons(Stella.SYM_STELLA_PROGN, trees.concatenate(Stella.NIL, Stella.NIL)));
    }
  }