# Heine-Borel Theorem ... Sohrab, Theorem 4.1.10 ... ...

#### Peter

##### Well-known member
MHB Site Helper
I am reading Houshang H. Sohrab's book: "Basic Real Analysis" (Second Edition).

I am focused on Chapter 4: Topology of [FONT=MathJax_AMS]R[/FONT] and Continuity ... ...

I need help in order to fully understand the proof of Theorem 4.1.10 ... ...

Theorem 4.1.10 and its proof read as follows:

In the above proof by Sohrab we read the following:

" ... ...Since $$\displaystyle [a, b]$$ is compact (by Proposition 4.1.9) we can find a finite subcover $$\displaystyle \mathcal{O}'' \subset \mathcal{O}'$$ ... ..."

My question is as follows:

If $$\displaystyle \mathcal{O}''$$ is a finite cover of $$\displaystyle [a, b]$$ then since $$\displaystyle K \subset [a, b]$$ surely $$\displaystyle \mathcal{O}'$$' is a finite cover of K also ... ... ?

BUT ... Sohrab is concerned about whether or not $$\displaystyle \mathcal{O}' \in \mathcal{O}''$$ or not ... ...

Can someone please explain what is going on ...

Peter

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The above post mentions Propositions 4.1.8 and 4.1.9 ... so I am providing text of the same ... as follows:

Hope that helps ...

Peter

#### Olinguito

##### Well-known member
Hi Peter.

$\cal O^{\prime\prime}$ is only a finite subcover of $\cal O^\prime$. In order to prove $K$ compact, we need to find a finite subcover of $\cal O$. That’s what’s going on.

#### Peter

##### Well-known member
MHB Site Helper
Hi Peter.

$\cal O^{\prime\prime}$ is only a finite subcover of $\cal O^\prime$. In order to prove $K$ compact, we need to find a finite subcover of $\cal O$. That’s what’s going on.

Thanks Olinguito ...

That clarified the matter ...

Most grateful for you help ...

Peter