Is FuncToFunc defined recursively in the excerpt below???

      private static interface FuncToTFunc<T> {
          Func<T> apply(FuncToTFunc<T> x);
      }

BTW, what is "x" in the above?

Also is Func defined mutually recursively with FuncToFunc in excerpt below?

      public static <T> Func<T> Y(final Func<Func<T>> r) {
        return ((FuncToTFunc<T>) f -> f.apply(f))
            .apply(
                f -> r.apply(
                    x -> f.apply(f).apply(x)));
      }