Meagre set

（重定向自Residual set）

In the mathematical fields of general topology and descriptive set theory, a meagre set (also called a meager set or a set of first category) is a set that, considered as a subset of a (usually larger) topological space, is in a precise sense small or negligible. The meagre subsets of a fixed space form a $\sigma$ -ideal of subsets; that is, any subset of a meagre set is meagre, and the union of countably many meagre sets is meagre.

单词	Residual set
释义	Residual set 英语百科 Meagre set （重定向自Residual set） In the mathematical fields of general topology and descriptive set theory, a meagre set (also called a meager set or a set of first category) is a set that, considered as a subset of a (usually larger) topological space, is in a precise sense small or negligible. The meagre subsets of a fixed space form a $\sigma$ -ideal of subsets; that is, any subset of a meagre set is meagre, and the union of countably many meagre sets is meagre.
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