Proving Regularity in Y through Closed Continuous Surjective Maps

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Homework Help Overview

The problem involves proving that if a closed continuous surjective map from a space X to a space Y has the property that the preimage of any point in Y is compact, then Y is regular if X is regular. The discussion centers around the concepts of regularity and compactness in topology.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the initial steps needed to approach the proof, with one participant expressing uncertainty about which information to utilize. Another suggests leveraging the compactness of the preimage to find disjoint neighborhoods. There is also a focus on how to translate open sets in X to Y while maintaining the necessary properties.

Discussion Status

The discussion is ongoing, with participants offering hints and exploring different aspects of the problem. There is a recognition of the need to connect the properties of neighborhoods in X to those in Y, but no consensus has been reached on the specific method to achieve this.

Contextual Notes

Participants are working within the constraints of the problem statement and are considering the implications of regularity and compactness without having resolved the proof. There is an acknowledgment of the challenge in transitioning from properties in X to those in Y.

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Homework Statement

Let f : X--> Y be a closed continuous surjective map such that f^(-1)(y) is compact.
Show that if X is regular, so is Y .

The Attempt at a Solution


I'm not sure which piece of info I need to use to start each of these. Any help with the proof would be really appreciated. I already figured out how to show that if X is Hausdorff , so is Y, but I can't figure out how to show it's regular.
 
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Pick a closed set C in Y. You know for every element x of f^(-1)(y) that x and the closed set f^(-1)(C) have nonoverlapping neighborhoods. Next use the most basic property of compact sets. That's a hint to get you started.
 
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Okay, so I can use compactness to find a finite open covering that is disjoint from the other neighborhood. How can I turn these open sets in X into disjoint open sets in Y? Since the mapping is closed, I have tried to use complements to find the proper disjoint sets, but it is not working.
 
Take the union of the neighborhoods in the finite covering and call it U. Take the intersection of the corresponding neighborhoods of f^(-1)(C) and call it V. Now map those two neighborhoods into Y. What's not working? Oh, I see. So far we only have that f^(-1)(y) and f(-1)(C) are separated in X. Hmmmm.
 
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