Baby Rudin - Cantor Set. A question.

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In summary, the author is discussing the concept of the Cantor set and its properties. He mentions that the Cantor set cannot contain any segments and provides a proof for this claim. He also clarifies that the statement 3^-m < (beta - alpha)/6 is a hypothesis, not a conclusion. The author also suggests a more rigorous statement regarding the Cantor set having an empty interior and explains how this can be proven using the base-3 expansion of points in the set.
  • #1
julypraise
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I do not get the second sentence of the paragraph in the image. What segment does he refer to when he says "no segment"? And why is it 3^-m < (beta - alpha)/6? Why 6?
 

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  • #2
He is just saying that the Cantor set can not contain any segments. The proof is that
any segment must contain a middle third (or ninth or 27'th or ...) and thus can not be contained in the Cantor set.

The proof seems a bit pedantic. Try doing it yourself without the book.
 
  • #3
julypraise said:
I do not get the second sentence of the paragraph in the image. What segment does he refer to when he says "no segment"?
Not surprizingly, when he says "no segment", he is not talking about any segment!

And why is it 3^-m < (beta - alpha)/6? Why 6?
Again, you are misunderstanding. He is not saying that 3^-m< (beta- alpha/6, he says "If" 3^-m< (beta- alpha)/6. That is an hypothesis.
 
  • #4
I think the more rigorous statement of whatthe author is claiming is that the Cantor set has an empty interior. In R--where the Cantor set sits -- it means that , for any c in the Cantor set, and any e>0 , the interval:

(c-e,c+e)

Is not contained in the Cantor set.

You can use the characterization of the points of C in terms of their base-3 expansion to show this.
 

1. What is the Cantor set?

The Cantor set is a mathematical set that is constructed by repeatedly removing the middle third of a line segment. The resulting set is a perfect example of a fractal, as it has a self-similar structure at different scales. It was first described by German mathematician Georg Cantor in 1883.

2. How is the Cantor set related to Baby Rudin?

The Cantor set is often mentioned in the famous textbook "Principles of Mathematical Analysis" by Walter Rudin, also known as "Baby Rudin". In this book, the Cantor set is used as an example to introduce the concept of a perfect set, which is a set that is closed, contains no isolated points, and has a cardinality of the continuum.

3. Why is the Cantor set important in mathematics?

The Cantor set is important in mathematics because it serves as a fundamental example of a set with interesting properties such as being uncountable, having a measure of zero, and being nowhere dense. It also has connections to other areas of mathematics, such as fractal geometry and topology.

4. Is the Cantor set a fractal?

Yes, the Cantor set is considered a fractal due to its self-similar structure at different scales. This means that as you zoom in on different parts of the set, you will see similar patterns repeating themselves. Fractals have applications in various fields, including computer graphics, biology, and physics.

5. How is the Cantor set constructed?

The Cantor set is constructed by starting with a line segment and repeatedly removing the middle third of each remaining line segment. This process is continued infinitely, resulting in a set that contains infinitely many points but has a measure of zero. The construction of the Cantor set can also be generalized to higher dimensions.

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