TCP 替你做了几件

net_05 n01_q3 说 UDP 不保证「到不到、顺序、重复」，n05_q3 说应用层补齐三样就重新发明了 TCP。把七件事列出来，数数 TCP 替你做了几件、剩下哪些还得你自己管：

things = ["丢了补发", "乱了排好", "重复丢掉", "对方在不在", "消息边界", "多久能到", "读没读"]
tcp = {"丢了补发", "乱了排好", "重复丢掉", "对方在不在"}
print(str(len(tcp)) + "/" + ",".join(t for t in things if t not in tcp))