Non-Surjective Continuous Function in Compact Hausdorff Space?

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SUMMARY

The discussion centers on proving that for a continuous function \( f: X \to X \) defined on a compact Hausdorff space \( (X, \tau) \) that is not surjective, there exists a nonempty proper subset \( S \subset X \) such that \( f(S) = S \). Participants suggest considering the sets \( S_n = f^{\circ n}(X) \) and note that these sets are closed and compact due to the properties of continuous functions on compact spaces. The proof hinges on the nested nature of the sets \( S_n \) and the limit of these sets, leading to the conclusion that \( S \) is non-empty and satisfies the required condition.

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  • Understanding of compact Hausdorff spaces
  • Knowledge of continuous functions and their properties
  • Familiarity with the concept of nested sets in topology
  • Basic grasp of limits and convergence in topological spaces
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This discussion is beneficial for students and researchers in topology, particularly those studying properties of continuous functions in compact spaces, as well as mathematicians interested in fixed point theorems and their applications.

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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) =<br /> 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.
 
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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?
 
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.
 

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