Proving Uniform Continuity on a Closed Bounded Interval

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Discussion Overview

The discussion revolves around proving that a function \( f \) is uniformly continuous on a closed bounded interval \([a,b]\) given its continuity on that interval. The scope includes theoretical aspects of continuity, proofs, and related concepts such as compactness and sequences.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about proving uniform continuity without relying on concepts like compactness or the Heine-Borel theorem.
  • Another participant expresses skepticism about proving uniform continuity without the mentioned concepts, suggesting that understanding the distinction between 'normal' and 'uniform' continuity might be more feasible.
  • A participant proposes a method involving the construction of a sequence with no limit point in \([a,b]\) to argue against uniform continuity, questioning the foundational knowledge of sequences in the context of continuity.
  • Another participant suggests a proof technique involving subdivision of intervals to demonstrate a contradiction regarding continuity, emphasizing the construction of an infinite decimal that leads to a point of discontinuity.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of advanced concepts for proving uniform continuity, with some advocating for their inclusion and others questioning their relevance. The discussion remains unresolved regarding the best approach to the proof.

Contextual Notes

Limitations include the potential dependence on definitions of continuity and uniform continuity, as well as the unresolved nature of the proof techniques discussed.

irony of truth
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How do I prove that when a function f is continuous on a closed bounded interval [a,b], it is uniformly continuous on that interval?

Actually, I have found some proofs to this but I have not tackled about compact, Heine-Borel theorem, metric spaces, sequences and series, etc. in my class..
 
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The proof I have uses Heine-Borel, so I assume you won't be interested in that one.

I do doubt thought that you would be able to rigourously proof it without any of the concepts or theorems you mentioned, unless you're just interested in explaining it, the difference between 'normal' and 'uniform' continuity.
 
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Suppose it is not unifromly continuous, construct a sequence with no limit point in [a,b] surely you know enough abuot sequences to be able to konw that that is impossible? (no one does continuity before sequences, surely?)
 
Thank you for the help...
 
you can make matt's proof concrete by the trick of subdivision. I.e. on the interval [0,1] if you have an infinite collection of points then there is an infinite number of them in some subinterv of length 1/10, say between .1 and .2.

Then ther is also an infinite num=ber of them between say .11 and .12.


and so on. Eventually (after an infinite number of steps) you construct an infinite decimkal, i.e. a real number, with an infinite number of these points in every neighborhood.

Since the infinite sequence was chosen in the beginning to be points hwere the function was "less and less continuous" i.e. needing bigger and bigger delta for a given epsilon, you deduce that your function is not continuous at all at the coinstructed point. a contradiction.
 

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