## 5.2. Compact and Perfect Sets

### Definition 5.2.4: Open Cover

Let

**S**be a set of real numbers. An open cover of**S**is a collection**C**of open sets such that**S****C**. The collection**C**of open sets is said to cover the set**S**.
A subset of sets from the collection **C** that still covers
the set **S** is called a subcovering of **S**.