# Kuratowski's closure-complement problem

> theorem that the monoid generated by taking closures and complements of a given set in a topological space has size at most 14, attained by e.g. the set (0, 1) ∪ (1, 2) ∪ {3} ∪ ([4, 5] ∩ ℚ) of reals

**Wikidata**: [Q6445654](https://www.wikidata.org/wiki/Q6445654)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Kuratowski's_closure-complement_problem)  
**Source**: https://4ort.xyz/entity/kuratowski-s-closure-complement-problem


## References

1. Freebase Data Dumps. 2013