402.3A4 Accumulation Points and Closure of a Set

Boundary points of a set that come from beyond the set itself are called accumulation points. We use this definition to define the closure of a set and investigate the spectrum between openness and closedness. See the playlist: http://matthematics.com/real

0:00 Introduction
2:30 Motivation for Accumulation Points
6:37 Definition of Accumulation Points
7:32 Interior Points are Accumulation Points
11:54 The Derived Set of A
13:08 The Closure of A
14:21 Summary of Types of Points, Openness, Closedness