The set A⊂RA\subset \mathbb RA⊂R is an interval if for all a,b∈Aa,b \in Aa,b∈A with a<ba<ba<b and x∈Rx\in \mathbb Rx∈R, a<x<b ⟹ x∈A.a<x<b \implies x\in A.a<x<b⟹x∈A.
Wikidata ID: Q185148