Compact Hausdorff space.

In summary, the problem asks to prove the existence of a nonempty proper subset S \subset X such that f(S) = S, given a compact Hausdorff space (X,\tau) and a continuous but not surjective function f : X \to X. The hint suggests considering the subspaces S_n := f^{\circ n}(X) where f^{\circ n} := f \circ \cdots \circ f (n times). The solution involves defining S as the limit of the S_n sets and using the fact that f(S) = lim f(S_n) to show that f(S) = S. The properties of S_n being closed and compact are also mentioned but not utilized in the solution
  • #1
complexnumber
62
0

Homework Statement



Let [tex](X,\tau)[/tex] be a compact Hausdorff space,
and let [tex]f : X \to X[/tex] be continuous, but not surjective. Prove that
there is a nonempty proper subset [tex]S \subset X[/tex] such that [tex]f(S) =
S[/tex]. [Hint: Consider the subspaces [tex]S_n := f^{\circ n}(X)[/tex] where
[tex]f^{\circ n} := f \circ \cdots \circ f[/tex] ([tex]n[/tex] times)].

Homework Equations





The Attempt at a Solution



If such [tex]S[/tex] exists then [tex]f^{\circ n}(S) = S[/tex]. How should I use this in the proof? I don't have any clue where to start.
 
Physics news on Phys.org
  • #2
What can you say about the sets S_n? For example, are they nested? What do you know about the continuous image of a compact set?
 
  • #3
Sorry for digging up an old thread, but I am stuck on the same problem.

I let S = lim S_n so we have f(S) = f(lim S_n) = lim f(S_n) = lim S_{n+1} = S. Obvisouly S is non-empty since each f(S_n) is not empty.

I am not sure if I got it right. We know that each S_n is closed and compact since X is a compact Hausdorff space and f is continuous, but I didnt use this property at all in my solution.

Any help would be appreciated.
 

1. What is a Compact Hausdorff space?

A Compact Hausdorff space is a topological space that satisfies two important properties: compactness and Hausdorffness. Compactness means that any open cover of the space has a finite subcover, while Hausdorffness means that any two distinct points in the space have disjoint open neighborhoods.

2. Why is compactness important in a Hausdorff space?

Compactness is important in a Hausdorff space because it ensures that the space is well-behaved and has nice topological properties. For example, compactness guarantees that the space is closed and bounded, making it easier to study and analyze. Additionally, many important theorems and results in topology and analysis require compactness as a condition.

3. How is compactness different from connectedness?

Compactness and connectedness are two distinct properties of a topological space. While compactness deals with the size and behavior of open covers, connectedness deals with the structure and connectivity of the space. A space can be both compact and connected, or it can have one property without the other.

4. What are some examples of Compact Hausdorff spaces?

Some common examples of Compact Hausdorff spaces include the closed unit interval [0,1], the Cantor set, and the unit sphere in n-dimensional Euclidean space. Other examples include the product of two compact Hausdorff spaces and the Stone-Cech compactification of a discrete space.

5. How is the Compact Hausdorff property useful in mathematics?

The Compact Hausdorff property is useful in mathematics for several reasons. First, it allows for the application of important theorems and results in topology, such as the Tychonoff theorem and the Baire category theorem. Secondly, many mathematical structures and objects, such as topological groups and measure spaces, require the space to be compact Hausdorff in order to have well-defined properties and behaviors. Lastly, compact Hausdorff spaces are often used in constructing and studying more complex spaces, such as manifolds and algebraic varieties.

Similar threads

  • Calculus and Beyond Homework Help
Replies
5
Views
829
  • Calculus and Beyond Homework Help
Replies
0
Views
449
  • Calculus and Beyond Homework Help
Replies
1
Views
504
  • Calculus and Beyond Homework Help
Replies
12
Views
1K
  • Calculus and Beyond Homework Help
Replies
12
Views
1K
  • Calculus and Beyond Homework Help
Replies
5
Views
1K
  • Calculus and Beyond Homework Help
Replies
6
Views
3K
  • Calculus and Beyond Homework Help
Replies
18
Views
1K
  • Calculus and Beyond Homework Help
Replies
5
Views
620
  • Calculus and Beyond Homework Help
Replies
1
Views
460
Back
Top