# Sufficient Conditions for a Covering Space

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• Euge
In summary, sufficient conditions for a covering space include having a continuous and surjective map, having a locally path-connected and semilocally simply connected base space, and having a discrete and properly discontinuous action of the fundamental group of the base space on the covering space. A non-connected space can also be a covering space as long as the connected components correspond to those of the base space and the sufficient conditions are met. These conditions are important for preserving the properties of the base space in the covering space and for studying topological spaces and their fundamental groups. There are also different types of covering spaces with their own specific properties and applications, such as regular, universal, and Galois covering spaces. Covering spaces are closely related to fundamental groups,
Euge
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Prove that every surjective local homeomorphism ##\pi : \tilde{X} \to X## from a compact Hausdorff space ##\tilde{X}## to a Hausdorff space ##X## is a covering space.

jedishrfu, Greg Bernhardt and topsquark
Fix ##x\in X##. The fiber ##\pi^{-1}(x)## is a closed subset of the compact space ##\tilde{X}## so it is compact. Further, since ##\pi## is a local homeomorphism, ##\pi^{-1}(x)## is discrete. Therefore ##\pi^{-1}(x)## is a finite set, say ##\{\tilde{x}_1,\ldots, \tilde{x}_n\}##. For each index ##i\in \{1,\ldots, n\}##, there are open neighborhoods ##U_{i} \ni \tilde{x}_i## and ##V_{i}\ni x## such that ##\pi## restricts to a homeomorphism from ##U_{i}## onto ##V_{i}##. Since ##\tilde{X}## is Hausdorff, we may assume the ##U_{i}## are disjoint. Then ##O := \bigcup_{i = 1}^n V_i - \pi(\tilde{X}\setminus \bigcup_{i = 1}^n U_i)## is a covering neighborhood of ##x##, as desired.

topsquark

## 1. What are sufficient conditions for a covering space?

Sufficient conditions for a covering space include being a locally path-connected and semilocally simply connected space, having a discrete fundamental group, and having a universal cover.

## 2. How do these conditions ensure that a space is a covering space?

The conditions of being locally path-connected and semilocally simply connected ensure that the space has enough paths and loops to cover every point, while the discrete fundamental group guarantees that the covering map is injective. The existence of a universal cover then guarantees that the space is a covering space.

## 3. Can a space satisfy some but not all of these conditions and still be a covering space?

Yes, a space can satisfy some but not all of these conditions and still be a covering space. For example, a space can be locally path-connected and have a discrete fundamental group, but not be semilocally simply connected. In this case, the space may still be a covering space, but it would not be a universal cover.

## 4. Are these conditions necessary for a space to be a covering space?

No, these conditions are not necessary for a space to be a covering space. There are other conditions that can also ensure that a space is a covering space, such as being a regular covering space or being a covering space with a finite fundamental group.

## 5. How are these conditions used in practical applications of covering spaces?

These conditions are used in practical applications of covering spaces to determine if a given space is a covering space or to construct new covering spaces. They also help in understanding the properties and behavior of covering spaces, which can be applied in various fields such as topology, physics, and engineering.

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