英语词汇“Fσ set”是什么意思，翻译、用法及简单造句-英汉双解词典-英汉网

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单词	Fσ set
释义	Fσ set 中文百科 Fσ集数学上，一个F_σ集是可数个闭集的并集。F_σ集的记法是豪斯多夫在1914年出版的著作《Grundzüge der Mengenlehre》引入的。名称中的F来自法文的fermé，意思是闭（现在法文也称闭集为fermé），而σ来自德文的Summe，意思是和，在此指可数个集合的并集。 F_σ集的补集是G_δ集。可数多个F_σ集的并是F_σ集。有限多个F_σ集的交是F_σ集。F_σ和博雷尔分层中的 $\mathbf{\Sigma}^0_2$ 相同。英语百科 Fσ set Fσ集 In mathematics, an F_σ set (said F-sigma set) is a countable union of closed sets. The notation originated in France with F for fermé (French: closed) and σ for somme (French: sum, union). In metrizable spaces, every open set is an F_σ set. The complement of an F_σ set is a G_δ set. In a metrizable space, any closed set is a G_δ set.
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更新时间：2025/11/30 11:35:43