a04424ad2c06782ab47e5a67ee91766dc28ff1edd2acc7c1bf10d4c759d4d421e32ee1f2f9a021171b83eaf673c1bfhttps://math.stackexchange.com/questions/1757735/theorem-3-17-in-baby-rudin-infinite-limits-and-upper-and-lower-limits-of-real-s 에서 증명 찾아서 이해하긴 했는데 너무 복잡함.. 좀 더 간단한 증명은 없을까요?