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

          prognTree.secondSetter(null);
          return (tree);
        }
      default:
        return (prognTree);
    }
  }