作者ericakk (無緣台大數學人)
看板Math
標題[高微] 關於finite set
時間Mon Mar 1 09:45:46 2010
在看Rudin高微拓樸學那邊
有一個Corollary提到： A finite point set has no limit points.
緊接著又提到：A finite set is closed.
然後我就產生這樣疑惑：因為 finite set 沒有limit points，
且closed 是用limit points 去定義
那我們怎麼可說 ：A finite set is closed???
謝謝回答:)
--
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 58.115.68.9
推 yusd24 :因為 finite set 沒有 limit point 03/01 09:56
→ yusd24 :所以 finite set 當然是 closed.. 03/01 09:57
→ yusd24 :就自動符合 "limit points are contained in A" 03/01 09:57
→ yusd24 :A is a finite set 的定義 03/01 09:58
推 euphrate :A' = ψ ﹙ A ==> A is closed 03/01 11:06