Bi-interpretation in set theory, Bristol, February 2020

This will be a talk for the Logic and Set Theory seminar at the University of Bristol, on 25 February, 2020.

Abstract: In contrast to the robust mutual interpretability phenomenon in set theory, Ali Enayat proved that bi-interpretation is absent: distinct theories extending ZF are never bi-interpretable and models of ZF are bi-interpretable only when they are isomorphic. Nevertheless, for natural weaker set theories, we prove, including Zermelo-Fraenkel set theory ZFC- without power set and Zermelo set theory Z, there are nontrivial instances of bi-interpretation. Specifically, there are well-founded models of ZFC- that are bi-interpretable, but not isomorphic—even $\langle H_{\omega_1},\in\rangle$ and $\langle H_{\omega_2},\in\rangle$ can be bi-interpretable—and there are distinct bi-interpretable theories extending ZFC-. Similarly, using a construction of Mathias, we prove that every model of ZF is bi-interpretable with a model of Zermelo set theory in which the replacement axiom fails. This is joint work with Alfredo Roque Freire.

Bi-interpretation in weak set theories

  • J. D. Hamkins and A. R. Freire, “Bi-interpretation in weak set theories,” Mathematics arXiv, 2020.  
    author = {Joel David Hamkins and Alfredo Roque Freire},
    title = {Bi-interpretation in weak set theories},
    journal = {Mathematics arXiv},
    year = {2020},
    volume = {},
    number = {},
    pages = {},
    month = {},
    note = {},
    abstract = {},
    keywords = {},
    source = {},
    doi = {},
    url = {},
    eprint = {2001.05262},
    archivePrefix = {arXiv},
    primaryClass = {math.LO},

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