The cumulative hierarchy and the real numbers

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SUMMARY

The cumulative hierarchy is defined as $V_0=\emptyset$, $V_{\alpha+1}=\mathcal{P}(V_\alpha)$, and for limit ordinals $\lambda$, $V_\lambda=\bigcup_{\alpha<\lambda} V_\alpha$. This structure builds sets iteratively, leading to a set of size $|\mathbb{R}|$ at $V_{\omega+2}$. The construction of real numbers can proceed through Dedekind cuts or Cauchy sequences. However, the well-foundedness of the sets in the hierarchy raises questions about the existence of $\mathbb{R}$ within this framework.

PREREQUISITES
  • Understanding of set theory and ordinals
  • Familiarity with power sets and unions in set construction
  • Knowledge of Dedekind cuts and Cauchy sequences for real number construction
  • Concept of well-foundedness in set theory
NEXT STEPS
  • Study the properties of ordinals and their role in set theory
  • Research the implications of well-foundedness in the cumulative hierarchy
  • Explore the construction of real numbers using Dedekind cuts and Cauchy sequences
  • Examine the relationship between power sets and well-ordering
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Mathematicians, logicians, and students of set theory who are interested in the foundations of real numbers and the structure of the cumulative hierarchy.

hmmmmm
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We define the cumulative hierarchy as:

$V_0=\emptyset$

$V_{\alpha+1}=\mathcal{P}(V_\alpha)$

If $\lambda$ is a limit ordinal then $V_\lambda=\bigcup_{\alpha<\lambda} V_\alpha$

Then we have a picture of a big V where we keep building sets up from previous ones and each $V_\alpha$ is the class (set?) of all sets formed from the previous stages.

Now I am wondering how we get from here to a construction of the real numbers? I can see that we will have a set of size $|\mathbb{R}|$ by $V_{\omega+2}$ and then we could go on to construct the reals formally via dedekind cuts of cauchy sequences. However are the sets in the hierarchy well founded in which case $\mathbb{R}$ would not be there?

Thanks for any help
 
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I'm not too sure how to mark a thread as solved or something but my confusion here came from thinking that unions and power sets preserved well ordering, which they do not
 

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