推 APM99 :of course 10/02 18:02
推 jacky7987 :後面那者你也可以直接取A當成nbh就好啦 10/02 18:02
→ mikechan :後者neighborhood不一定要是開集 10/02 18:13
(X,T) a topological space
neigborhood of x(belongs to X)
看過兩個定義
一個是open set contains x (Royden用這個定義)
還有一個是只要包含A且A是open set contains x就算neighborhood(Folland用這個定義)
這兩個neighborhood定義建造出來的理論會一樣嘛?(比方說base,convergent seq,
first countable等等的定義都要用到neighborhood)
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