# sigma-ring

> Family closed under countable unions and relative complements

**Wikidata**: [Q3123369](https://www.wikidata.org/wiki/Q3123369)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Sigma-ring)  
**Source**: https://4ort.xyz/entity/sigma-ring


## References

1. Freebase Data Dumps. 2013