我愛陳嘉靖
2018-12-7 14:25:16
If X is the Euclidean space R, then the closure of the set Q of rational numbers is the whole space R. We say that Q is dense in R.
18歲嫩處女
2018-12-7 14:26:55
此回覆已被刪除
我愛陳嘉靖
2018-12-7 14:27:50
the closure of the set A is the union of A and its boundary