Why are linearly ordered R and R/{0} not isomophic?

In summary, the conversation discusses the proof of a set in R/{0} that has an upper bound but no least upper bound. It is stated that this set does not exist in the linearly ordered R. The conversation also mentions the compactness of the set [-1,0] and how removing the zero results in the loss of compactness and the absence of a maximum. The conversation concludes by mentioning that the Real Line with zero deleted does not have a smallest positive number, which is why it does not have a tight upper bound on negative numbers. The main point is that while both ##\mathbb R## and ##\mathbb R /{0}## are open sets, the former is connected while the latter is not
  • #1
QuasarBoy543298
32
2
i saw a proof that said “in R/{0} , the set [-1,0) has an upper bound ,but no least upper bound. no such set exists in linearly ordered R” ,but i could not understand it.
 
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  • #2
so ##[-1,0]## is compact and using the identity function has a maximum at zero. If you delete the zero you lose compactness and there is no longer a maximum.
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edit:
I think I misread this. The issue is that the Real Line with zero deleted doesn't have a smallest positive number for the same reason it doesn't have biggest (i.e. smallest magnitude) negative number. Any non-negative number is an upper bound of ##[-1,0)## but the issue is that if you have ##0## removed from the real line, you must use positive numbers and there isn't a smallest positive number hence no tight upper bound on negative numbers.

The point, I suppose is that ##\mathbb R## and ##\mathbb R /{0}## are both open sets but the former is connected while the latter is not
 
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Related to Why are linearly ordered R and R/{0} not isomophic?

1. Why are linearly ordered R and R/{0} not isomorphic?

The main reason for this is the presence of a zero element in R, which does not exist in R/{0}. Isomorphic structures must preserve the algebraic properties of their elements, but since R/{0} does not have a zero element, it cannot be isomorphic to R.

2. How does the presence of a zero element affect the isomorphism between R and R/{0}?

The zero element plays a crucial role in the algebraic structure of R, as it satisfies certain properties such as being an additive identity. The absence of a zero element in R/{0} means that the two structures cannot be mapped onto each other in a way that preserves their algebraic properties.

3. Can there be an isomorphism between R and R/{0} if we remove the zero element from R?

No, even if we remove the zero element from R, the structures would still not be isomorphic. This is because the presence or absence of a zero element fundamentally changes the algebraic properties of the structures, making them incompatible for isomorphism.

4. Are there any other differences between R and R/{0} that prevent them from being isomorphic?

Apart from the absence of a zero element, there are other differences between R and R/{0} that make them non-isomorphic. For example, R is a field, while R/{0} is not, as it does not have multiplicative inverses for all elements (since the zero element is excluded).

5. Is there any significance to studying the non-isomorphism between R and R/{0}?

Yes, understanding the reasons for the non-isomorphism between R and R/{0} helps us gain a deeper understanding of the algebraic structure of these two sets. It also highlights the importance of certain elements, such as the zero element, in determining the properties and relationships within a mathematical structure.

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