second-countable space

C2 可数公理

Geometry & Topology · Undergraduate · Mathematics Resources editorial compilation (AI-assisted)

Other names / variants: second countability

Translation evidence: Literature usage

Meaning in context

A topological space whose topology has a countable basis.

其拓扑具有可数基的拓扑空间。

Example

Rational open intervals give a countable basis for R\mathbb R.

Usage and distinctions

Second countability is global; an uncountable discrete space is first countable but not second countable. C2 follows the cited notation.

Recommended reading in this subject · Preparation & skip guidance

Definition sources

  1. Anton Petrunin — A minimalist intro to topologyChapter 8D, Countable base; 9E, Comments · Checked 2026-10-14

Translation sources

  1. Bao Zhiqiang — Peking University topology syllabus第2周9月26日，主要概念：C_{2} 可数公理 · Checked 2026-10-14
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