Interior

analysis

Definition

Interior

Let $I=[a,b]$ be a closed interval. Then the open interval $(a,b)$ is called the interior of $I$ and is denoted as $\mathring{I}$. The elements of $x\in \mathring{I}$ are called inner points or interior points.

Analogously, the interior of a set can be defined as the union of disjunctive intervals.