Room P3.10, Mathematics Building Instituto Superior Técnicohttps://tecnico.ulisboa.pt

, University of Chicago

Escaping Tennenbaum’s Theorem

Tennenbaum's theorem states that PA does not admit any nonstandard computable model. In 2022, Fedor Pakhomov proved that this theorem is fragile in regards to how PA is expressed, by constructing a theory that is definitionally equivalent to PA (roughly: “it’s PA but with a different choice of signature”) for which there is a computable nonstandard model. I will introduce the audience to this result and, time allowing, present the way in which we have been able to improve on Pakhomov's original construction and some remaining open questions.