Prove that every regular Lindelöf space is normal

In summary, the conversation discusses proving the normality of every regular Lindelöf space. The speaker mentions using a theorem that states every regular space with a countable basis is normal and suggests referencing Theorem 32.1 in Munkres for the proof. The speaker then outlines the proof, mentioning one variation and suggesting to refer to the book for the full proof. The other participant responds with appreciation for the proof.
  • #1
radou
Homework Helper
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Homework Statement



So, one needs to prove that every regular Lindelöf space is normal, exactly as the title suggests.

The Attempt at a Solution



I used the following theorem:

Every regular space with a countable basis is normal.

Now, what we need to prove can be proved very similarily to the proof of the theorem above. It's Theorem 32.1., page 200, in Munkres.

What I had in mind:

The proof is exactly the same, with one variation.

Let B be a basis for X. We choose a basis element contained in V for every x in A. Now, for any x in X\A, choose a basis element containing X. This collection forms an open cover for X, and since X is Lindelöf, it has a countable subcollection. So, the subcollection of all the basis elements for the elements of A is countable. Hence, the rest of the proof is the same.

I hope it won't be a problem to open Munkres and look at the proof, since it was too long to type, so I decided to be practical.

Thanks in advance.
 
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  • #2
As usual, this is a perfect little proof :smile:
 
  • #3
OK, thanks! It was kind of obvious to use this theorem.
 

1. What is a Lindelöf space?

A Lindelöf space is a topological space in which every open cover has a countable subcover. In simpler terms, this means that every open cover (a collection of sets that covers the whole space) can be reduced to a countable number of sets that still cover the space.

2. What is a regular space?

A regular space is a topological space in which points and closed sets can be separated by open sets. This means that for any point and any closed set that does not contain the point, there exist two disjoint open sets - one containing the point and one containing the closed set.

3. What does it mean for a space to be normal?

A normal space is a topological space in which any two disjoint closed sets can be separated by open sets. This means that for any two closed sets that do not intersect, there exist two disjoint open sets - one containing one of the closed sets and one containing the other.

4. Why is it important to prove that every regular Lindelöf space is normal?

This proof is important because it shows that the properties of regularity and Lindelöfness are enough to guarantee the property of normality. This is useful in many areas of mathematics, as it allows us to apply results and theorems that are specific to normal spaces to a wider class of spaces.

5. What is the significance of this proof in general topology?

This proof is significant in general topology because it demonstrates the relationship between different topological properties and helps us better understand the structure of topological spaces. It also allows us to generalize results and theorems to a wider class of spaces, making it a useful tool in various areas of mathematics.

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