Interior and exterior

The interior $I n t (𝑆)$ of a subset $𝑆$ of a topological space $𝑋$ is the union of all subsets of $𝑆$ that are open in $𝑋$ , i.e. it is the largest open subset of $𝑆$ (which may be $𝑆$ itself). topology The exterior is simply the interior of the compliment $𝑋 ∖ 𝑆$ , or alternatively it is the compliment of the closure of $𝑆$ . topology