Interior and Closure of Sets – Lecture 10 (Topology)

Let A ⊆ X in a topological space (X, τ). How is the interior int(A) defined in this lecture?

1. A.The smallest open set containing A
2. B.The set A with its boundary points removed
3. C.The union of all open subsets of A
4. D.The intersection of all open sets that meet A