The set-theoretic Kaufmann–Clote question
Let M be the set theory obtained from ZF by removing the collection scheme, restricting separation to Δ0-formulae and adding an axiom asserting that every set is contained in a transitive set. Let Πn-Collection denote the restriction of the collection scheme to Πn-formulae. We prove that for n≥1, if M is a model of M+Πn-Collection+V=L and N is a topless Σn+1-elementary end extension of M that satisfies Πn−1-Collection, then Πn+1-Collection holds in M. Here topless indicates that N contains an ordinal that is not in M, but no least ordinal that is not in M. This result is used to show that for n≥1, the minimum model of M+Πn-Collection has no Σn+1-elementary end extension that satisfies Πn−1-Collection, providing a negative answer to the generalisation of a question posed by Kaufmann.
Authors
- Zachiri McKenzie (ORCID: https://orcid.org/0000-0003-0807-9561)
Institutions
- University of Chester (GB)
Publication Details
- Journal
- Fundamenta Mathematicae
- Published
- 2026-09-17
- DOI
- https://doi.org/10.4064/fm250717-23-2
- Primary Topic
- Advanced Topology and Set Theory
- Type
- article
- Field-Weighted Citation Impact
- 0.00