# filter

> in order theory, a nonempty, downward‐directed, upward‐closed subset of a preordered set

**Wikidata**: [Q1052692](https://www.wikidata.org/wiki/Q1052692)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Filter_(mathematics))  
**Source**: https://4ort.xyz/entity/filter-q1052692-2


## References

1. Freebase Data Dumps. 2013