Intermediate models with deep failure of choice
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866929406011768832 |
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| author | Hayut, Yair Shani, Assaf |
| author_facet | Hayut, Yair Shani, Assaf |
| contents | The following question was asked by Grigorieff: Suppose $V$ is a ZFC model and $V[G]$ is a set-generic extension of $V$. Can there be a ZF model $N$ so that $V\subset N \subset V[G]$ yet $N$ is not equal to $V(A)$ for any set $A\in V[G]$? The first such model was constructed by Karagila. This is the so-called \emph{Bristol model}, an intermediate model between $L$ and $L[c]$ where $c$ is a Cohen-generic real over $L$. Karagila further proves that the Kinna-Wager degree is unbounded in this model.
We prove that such an intermediate extension can be found in a Cohen-generic extension of \emph{any} ground model, fully resolving Grigorieff's question. That is, let $V$ be \emph{any} ZF model and $c$ a Cohen-generic real over $V$. We prove that there is an intermediate ZF-model $V\subset N \subset V[c]$ so that $N$ is not equal to $V(A)$ for any set $A\in V[c]$, the Kinna-Wagner degree of $N$ is unbounded and, in particular, no set forcing in $N$ forces the axiom of choice.
Therefore, there are class many different intermediate models of ZF between $V$ and $V[c]$. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2407_02033 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Intermediate models with deep failure of choice Hayut, Yair Shani, Assaf Logic 03E25, 03E35 The following question was asked by Grigorieff: Suppose $V$ is a ZFC model and $V[G]$ is a set-generic extension of $V$. Can there be a ZF model $N$ so that $V\subset N \subset V[G]$ yet $N$ is not equal to $V(A)$ for any set $A\in V[G]$? The first such model was constructed by Karagila. This is the so-called \emph{Bristol model}, an intermediate model between $L$ and $L[c]$ where $c$ is a Cohen-generic real over $L$. Karagila further proves that the Kinna-Wager degree is unbounded in this model. We prove that such an intermediate extension can be found in a Cohen-generic extension of \emph{any} ground model, fully resolving Grigorieff's question. That is, let $V$ be \emph{any} ZF model and $c$ a Cohen-generic real over $V$. We prove that there is an intermediate ZF-model $V\subset N \subset V[c]$ so that $N$ is not equal to $V(A)$ for any set $A\in V[c]$, the Kinna-Wagner degree of $N$ is unbounded and, in particular, no set forcing in $N$ forces the axiom of choice. Therefore, there are class many different intermediate models of ZF between $V$ and $V[c]$. |
| title | Intermediate models with deep failure of choice |
| topic | Logic 03E25, 03E35 |
| url | https://arxiv.org/abs/2407.02033 |