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来自维基百科,自由的百科全书
第二可數空間是指有一個可數基的拓撲空間,我們也將「具備可數基」這一性質當作一條公理(第二可數性公理)放在第二可數空間的定義中(與「有限交,任意並」一同)。
Seamless Wikipedia browsing. On steroids.
Every time you click a link to Wikipedia, Wiktionary or Wikiquote in your browser's search results, it will show the modern Wikiwand interface.
Wikiwand extension is a five stars, simple, with minimum permission required to keep your browsing private, safe and transparent.