A question on Cantor's second diagonalization argument

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Cantor's second diagonalization argument demonstrates that the set of real numbers is uncountably infinite by showing that any assumed complete enumeration of real numbers in the interval (0,1) must be incomplete. The argument constructs a new real number that differs from each number in the list at the nth decimal place, proving it cannot be included in the enumeration. The discussion raises questions about the validity of Cantor's argument, suggesting that a new list can be constructed that appears to avoid Cantor's diagonalization. However, participants clarify that any countable list can be rewritten as a sequence, and Cantor's proof still applies. Ultimately, the argument reinforces that there are more real numbers than natural numbers, affirming the uncountability of the reals.
  • #31
When we have a complete list of rational numbers, represented by their decimal form, then Cantor's function result cannot be but an irrational number.

I think we have here some interesting state, because if what I wrote holds, it means that there can be some difference between aleph0 and aleph0-1, which is not quantitative but structural.

It means that if even one of the rational numbers is missing, we have the ability to define some rational number (repetitions over scales) as Cantor's function result.

But when we have a complete list of rational numbers, represented by their decimal forms, then Cantor's function result cannot be but an irrational number (no repetitions over scales).

Is there some mathematical area which deals with this fine difference between aleph0 and aleph0-1 ?
 
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  • #32
If we take the next step we can ask what is the structural difference between 2^aleph0 and 2^aleph0-1 ?

We sow that Cantor's function can find some rational number as a result (repetitions over scales), only if our list is aleph0-1.

Because we have only one representation to all irrational numbers, which is the base value expansion, how can we be sure that we are not in the same situation, which has been found in the case of the rational numbers list ?

In the case of the rational numbers we have two representation forms of numbers that can be compared to each other and help us to find the complete list.

But this is not the case of all R numbers that can be represented by only one form.

What I mean is when we still find some R number which is not in the list, can't we say that it means that we have 2^aleph0-1 list, which is not the 2^aleph0 complete list?

In this case we call |R| the uncountable, but maybe the only reason is the fact that we don’t know how to represent 2^aleph0 numbers, and all we have is the representation of 2^aleph0-1 numbers.

I know that 2^aleph0-1 = 2^aleph0, but again I talking about the structural difference between |R| and |R|-1.
 
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  • #33
In this case we call |R| the uncountable, but maybe the only reason is the fact that we don’t know how to represent 2^aleph0 numbers, and all we have is the representation of 2^aleph0-1 numbers.
No, we call R "uncountable" because it fits the precise mathematical definition of the word "uncountable".

I know that 2^aleph0-1 = 2^aleph0, but again I talking about the structural difference between |R| and |R|-1.
Then perhaps it would be a good idea for you to tell us exactly what YOU mean by "|R|-1", as well as what you mean by the "structure" of a cardinality.
 
  • #34
Hi HallsofIvy,

You wrote:
...it would be a good idea for you to tell us...
How is us ? Are you more then a one person ?

And if not, it looks like you think that you are the speaker of some group.

In this case what is the name of the group that gave you the job to be their speaker ?

My advice to you is: Please be more modest and less aggressive to the persons who write their point of views on any subject in this forum. You can learn it from Hurkyl.

First of all Math is a form of language and any language is a communication tool between persons, even if its gremial is rigorous. Please don't forget this important point.

Some persons are professionals and some are not, but you never know where some good idea can appear.

If you understand what I wrote about the structural difference between aleph0 and aleph0-1, then take this understanding and connect it to 2^aleph0 and 2^aleph0-1.

When the list has aleph0-1 numbers, then Cantor's function result can be some rational number (repetitions over scales).

When the list has aleph0 numbers, then Cantor's function result can't be but some irrational number (no repetitions over scales).

These are structural differences.

When the list has 2^aleph0-1 numbers, then Cantor's function result is some R number (repetitions, or no repetitions over scales).

When the list has 2^aleph0 numbers, then Cantor's function result is unknown.




Organic
 
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  • #35
Look up the phrase "editorial we". Yes, I was speaking on behalf of all the people (one or two at least) who read this thread. I certainly don't expect you to correspond with me personally to define your terms. I have no doubt that anyone reading this thread would appreciate you actually defining your terms.

You are completely correct that Hurkyl is "more modest and less aggressive" than I am. He perhaps still has some hopes that you will actually understand what he is saying.

I might also point out that you are not a good one to talk about being "more modest and less aggressive". You have repeatedly asserted that you knew for a fact that something that all professional mathematicians understand and accept is incorrect. You then give a lot of undefined terms and hand-waving to support that contention. Your basic argument appears to be "I do not understand this, therefore it is wrong."
 
  • #36
HallsofIvy,

Pay attention to the fact that you did not write a single word of what I wrote, after what I wrote personally to you.

Because you are a professional mathematician, which is the mentor of the Homework help zone, I think that you can do more then just repeating on the words "non-sense".

For example, Hurkyl helped me to address some idea of mine in a formal definition.

It can be found here: https://www.physicsforums.com/showthread.php?s=&threadid=7315

Please instead of "close the doors" as your first step, I'll appreciate your professional help.


Thank you.


Organic
 
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