The set-theoretic Kaufmann-Clote question
The set-theoretic Kaufmann-Clote question
Let $\mathsf{M}$ be the set theory obtained from $\mathsf{ZF}$ by removing the collection scheme, restricting separation to $Î_0$-formulae and adding an axiom asserting that every set is contained in a transitive set. Let $Î _n\textsf{-Collection}$ denote the restriction of the collection scheme to $Î _n$-formulae. In this paper we prove that for $n \geq 1$, if $\mathcal{M}$ is a model of $\mathsf{M}+Î _n\textsf{-Collection}+\mathsf{V=L}$ and $\mathcal{N}$ is a $Σ_{n+1}$-elementary end extension of $\mathcal{M}$ that satisfies $Î _{n-1}\textsf{-Colelction}$ and that contains a new ordinal but no least new ordinal, then $Î _{n+1}\textsf{-Collection}$ holds in $\mathcal{M}$. This result is used to show that for $n \geq 1$, the minimum model of $\mathsf{M}+Î _n\textsf{-Collection}$ has no $Σ_{n+1}$-elementary end extension that satisfies $Î _{n-1}\textsf{-Collection}$, providing a negative answer to the generalisation of a question posed by Kaufmann.
Zachiri McKenzie
数学
Zachiri McKenzie.The set-theoretic Kaufmann-Clote question[EB/OL].(2025-07-01)[2025-07-21].https://arxiv.org/abs/2507.01176.点此复制
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