clopen

English

Wikipedia has an article on:
Wikipedia

Etymology

Blend of closed +‎ open.

Pronunciation

FACT 1. Disjoint closed subsets of ${\displaystyle \mathbb {N} ^{\mathbb {N} }}$ may be separated by disjoint clopen sets.
Theorem 3. 1) Every two disjoint closed sets in a totally disconnected compact space ${\displaystyle {\mathfrak {Q}}}$ are separated by disjoint clopen sets.