Showing that Increasing sequences of natural numbers is uncountable

In summary, the conversation discusses the proof that the set of all increasing sequences of natural numbers, denoted as A, is uncountable. The individual mentions using a diagonal argument and gives an example using real numbers between 0 and 1 with only 3s and 7s in their decimal expansions. This set is known as a Cantor set and is shown to be uncountable by a bijection between it and the set of infinite binary sequences. The conversation then suggests considering a bijection between infinite sequences of increasing natural numbers and infinite sequences of 0's and 1's in order to prove the uncountability of A. The individual acknowledges that this is what they were trying to convey and apologizes for being redundant
  • #1
renjean
7
0

Homework Statement


Show that A, the set of all increasing sequences of natural numbers is uncountable


Homework Equations


I know that the natural numbers themselves are countable.


The Attempt at a Solution


I am thinking of using some sort of diagonal argument to prove this.
 
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  • #2
Well take the example:

Let R denote the reals. Let R′ denote the set of real numbers, between 0 and 1, having decimal expansions that only involve 3s and 7s. s. (This set R′ is an example of what is called a Cantor set. ) There is a bijection between R′ and the set S of infinite binary sequences. For instance, the sequence 0101001.. is mapped to .3737337... Hence R′ is uncountable. Hope this gives you a clue on how to start.
 
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  • #3
You probably know how to show that the set of all infinite sequences of 0's and 1's is uncountable by a diagonal argument. Can you think of a bijection between infinite sequences of increasing natural numbers and infinite sequences of 0's and 1's?
 
  • #4
Dick said:
You probably know how to show that the set of all infinite sequences of 0's and 1's is uncountable by a diagonal argument. Can you think of a bijection between infinite sequences of increasing natural numbers and infinite sequences of 0's and 1's?


That's kind of what I was trying to tell him.
 
  • #5
mtayab1994 said:
That's kind of what I was trying to tell him.

Yes, I see that it was. Sorry to be redundant.
 
  • #6
Not a problem he's here for our help.
 
  • #7
That helps a lot! Thank you to the both of you.
 

FAQ: Showing that Increasing sequences of natural numbers is uncountable

What is the definition of an increasing sequence of natural numbers?

An increasing sequence of natural numbers is a sequence in which each term is larger than the previous one. For example, 1, 2, 3, 4, 5 is an increasing sequence of natural numbers.

How do you prove that increasing sequences of natural numbers are uncountable?

To prove that increasing sequences of natural numbers are uncountable, we can use the diagonalization argument. This involves assuming that there is a countable number of terms in the sequence and then constructing a new term that is not in the sequence, thus showing that the sequence is actually uncountable.

What is the significance of showing that increasing sequences of natural numbers are uncountable?

This result is significant because it demonstrates that there are infinite sets that are larger than the set of natural numbers. It also has implications in other areas of mathematics, such as set theory and analysis.

Can you provide an example of an increasing sequence of natural numbers that is uncountable?

One example of an increasing sequence of natural numbers that is uncountable is the sequence of powers of 2: 1, 2, 4, 8, 16, 32, ... This sequence is uncountable because it is infinite and each term is larger than the previous one.

Is there a connection between showing that increasing sequences of natural numbers are uncountable and the concept of infinity?

Yes, there is a strong connection between these two concepts. Proving that increasing sequences of natural numbers are uncountable demonstrates that there are infinitely many numbers that cannot be counted, which is a fundamental characteristic of infinity.

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