Intermediate models with deep failure of choice
Abstract
The following question was asked by Grigorieff: Suppose is a ZFC model and is a set-generic extension of . Can there be a ZF model so that yet is not equal to for any set ? The first such model was constructed by Karagila. This is the so-called \emph{Bristol model}, an intermediate model between and where is a Cohen-generic real over . 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 be \emph{any} ZF model and a Cohen-generic real over . We prove that there is an intermediate ZF-model so that is not equal to for any set , the Kinna-Wagner degree of is unbounded and, in particular, no set forcing in forces the axiom of choice. Therefore, there are class many different intermediate models of ZF between and .
Cite
@article{arxiv.2407.02033,
title = {Intermediate models with deep failure of choice},
author = {Yair Hayut and Assaf Shani},
journal= {arXiv preprint arXiv:2407.02033},
year = {2024}
}