# Lindelöf's lemma

> lemma that every open subset of the reals is a countable union of open intervals

**Wikidata**: [Q6552215](https://www.wikidata.org/wiki/Q6552215)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Lindelöf's_lemma)  
**Source**: https://4ort.xyz/entity/lindel-f-s-lemma