If we are only interested in some specific information, say, "was there a person of age n in the room?", keeping a list of all names and dates of births is unnecessary.
如果我们只感兴趣于某些特定信息，比如“有年龄 n 岁的人在屋子中吗？”，则必须保存所有人的名字和生日的列表是不必需的。