The Diagonal Method: Proving Sets are Infinite

In summary, the conversation discusses Cantor's diagonal argument, also known as the Diagonal Method, which proves that the natural numbers and real numbers do not have equal cardinality. The method involves singling out the diagonal terms of a list, and it is used to show that the reals are uncountable while the rationals are countable. The conversation also mentions constructing a bijection between integers and rationals, but it is noted that there is no such bijection. There are two variations of the proof, one of which uses a diagonal argument and the other uses the fact that rational numbers are a subset of pairs of integers.
  • #1
Aditya89
23
0
Can anybody tell me the Canter Method of proving that certain sets are infinite? It is called as "Diagonal Method".
 
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  • #3
Hey thanks, Zurtex! But from the first link, it does not become clear why it is called "Diagonal Method". Also, can you explain the link between first proof and second proof, please? Also, please tell me how to construct a bijection between Rationals & Reals.
 
  • #4
Aditya89 said:
Hey thanks, Zurtex! But from the first link, it does not become clear why it is called "Diagonal Method". Also, can you explain the link between first proof and second proof, please?

See the wiipedia article, step 5 in the proof singles out the 'diagonal' terms of the list. I only count one proof in the links he gave.

Aditya89 said:
Also, please tell me how to construct a bijection between Rationals & Reals.

There isn't one. The diagonal argument shows the reals are uncountable while the rationals are countable.
 
  • #5
Oh! I'm sorry for saying reals & rationals! It's integers and rationals! And why do you count only one proof?
 
  • #6
The rationals are famously countable, try constructing the proof yourself. There are two variants. One is anothert kind of diagonal argument, and the other is by remembering that rational numbers are a subset of the pairs of integers.
 

What is the Diagonal Method?

The Diagonal Method, also known as Cantor's Diagonal Argument, is a mathematical proof technique used to show that a given set is infinite. It was developed by mathematician Georg Cantor in the late 19th century.

How does the Diagonal Method work?

The Diagonal Method involves constructing a list of elements in a set and then creating a new element by changing each element in the list in a specific way. This new element is then shown to be different from every element in the original list, thus proving that the set is infinite.

What sets can be proven to be infinite using the Diagonal Method?

The Diagonal Method can be used to prove that any set that contains an infinite number of elements is infinite. This includes sets of natural numbers, real numbers, and even sets of infinite sequences.

Why is the Diagonal Method important?

The Diagonal Method is a powerful proof technique that has been used to solve many problems in mathematics, including the famous Continuum Hypothesis. It also helps us understand the concept of infinity and the properties of infinite sets.

Are there any limitations to the Diagonal Method?

While the Diagonal Method is a useful tool for proving sets are infinite, it cannot be used to prove the size or cardinality of a set. It also cannot be used to prove that a set is finite, as it only works for infinite sets.

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