June 1

**Münster Set Theory Seminar****Time:** Tuesday, June 1, 4:15pm CEST**Speaker:** No seminar this week**Title:** No seminar this week**Abstract:** No seminar this week**Information:** contact rds@wwu.de ahead of time in order to participate.

**Cornell Logic Seminar****Time:** Tuesday, June 2, 2:55pm New York time (20:55pm CEST)**Speaker:** TBA**Title:** TBA**Abstract:** TBA**Information:** contact solecki@cornell.edu ahead of time to participate.

May 27

**Jerusalem Set Theory Seminar****Time:** Wednesday, June 3, 11:00am (Israel Time)**Speaker:** TBA**Title:** TBA**Abstract:** TBA**Information:** contact omer.bn@mail.huji.ac.il ahead of time in order to participate.

**Paris-Lyon Séminaire de LogiqueTime:** Wednesday, June 3, 16:00-17:15 CEST

**Speaker:**Colin Jahel

**Title:**In 2005, Kechris, Pestov and Todorcevic exhibited a correspondence

between combinatorial properties of structures and dynamical properties

of their automorphism groups. In 2012, Angel, Kechris and Lyons used

this correspondence to show the unique ergodicity of all the actions of

some groups. In this talk, I will give an overview of the aforementioned

results and discuss recent work generalizing results of Angel, Kechris

and Lyons.

**Information:**Join via the link on the seminar webpage 10 minutes before the talk.

**Bristol Logic and Set Theory SeminarTime:** Wednesday, June 3, 14:00-15:30 (UK time)

**Speaker:**TBA

**Title:**TBA

**Abstract:**TBA

**Information:**Please contact Philip Welch (p.welch@bristol.ac.uk) ahead of time to participate.

**CUNY Set Theory Seminar****Time:** Wednesday, June 3, 7pm New York time (1am May 14 CEST)**Speaker: **Zachiri McKenzie**Title:** Initial self-embeddings of models of set theory: Part I**Abstract:** In the 1973 paper ‘Countable models of set theory’, H. Friedman’s investigation of embeddings between countable models of subsystems of ZF yields the following two striking results:

1. Every countable nonstandard model of PA is isomorphic to a proper initial segment of itself.

2. Every countable nonstandard model of a sufficiently strong subsystem of ZF is isomorphic to a proper initial segment that is a union of ranks of the original model.

Note that, in contrast to PA, in the context of set theory there are three alternative notions of ‘initial segment’: transitive subclass, transitive subclass that is closed under subsets and rank-initial segment. Paul Gorbow, in his Ph.D. thesis, systematically studies versions of H. Friedman’s self-embedding that yield isomorphisms between a countable nonstandard model of set theory and a rank-initial segment of itself. In these two talks I will discuss recent joint work with Ali Enayat that investigates models of set theory that are isomorphic to a transitive subclass of itself. We call the maps witnessing these isomorphisms ‘initial self-embeddings’. I will outline a proof of a refinement of H. Friedman’s Theorem that guarantees the existence of initial self-embeddings for certain subsystems of ZF without the powerset axiom. I will then discuss several examples including a nonstandard model of ZFC minus the powerset axiom that admits no initial self-embedding, and models that separate the three different notions of self-embedding for models of set theory. Finally, I will discuss two interesting applications of our version of H. Freidman’s Theorem. The first of these is a refinement of a result due to Quinsey that guarantees the existence of partially elementary proper transitive subclasses of non-standard models of ZF minus the powerset axiom. The second result shows that every countable model of ZF with a nonstandard natural number is isomorphic to a transitive subclass of the hereditarily countable sets of its own constructible universe.**Information:** The seminar will take place virtually. Please email Victoria Gitman (vgitman@nylogic.org) for the meeting id.

**Oxford Set Theory Seminar****Time:** Wednesday, June 3, 4pm UK time**Speaker:** TBA**Title:** TBA**Abstract:** TBA

**Information:** The seminar will take place virtually. Please email Sam Adam-Day at me@samadamday.com for the meeting id.

May 28

**Kurt Gödel Research Center Seminar** (organised by Ben Miller)**Time:** Thursday, June 4, 16:00 CEST

**Speaker:**Stefan Hoffelner (University of Münster, North Rhine-Westphalia, Germany)

**Title:**Forcing the Sigma^1_3-separation property

**Abstract:** The separation property, introduced in the 1920s, is a classical notion in descriptive set theory. It is well-known due to Moschovakis, that **Δ12**-determinacy implies the **Σ13**-separation property; yet **Δ12**-determinacy implies an inner model with a Woodin cardinal. The question whether the **Σ13**-separation property is consistent relative to just ZFC remained open however since Mathias’ “Surrealist Landscape”-paper. We show that one can force it over L.**Information:** Talk via zoom.

May 29

**CUNY Set Theory Seminar****Time:** Friday, June 5, 2pm New York time (8pm CEST)**Speaker:** Michał Godziszewski — Munich Center for Mathematical Philosophy**Title:** TBA**Abstract:** TBA**Information:** The seminar will take place virtually. Please email Victoria Gitman (vgitman@nylogic.org) for the meeting id.

**Toronto Set Theory Seminar****Time:** Friday, June 5, 1.30pm Toronto time (7.30pm CEST)**Speaker:**TBA**Title:** TBA**Abstract:** TBA**Information:** The seminar will take place virtually. ZOOM ID: https://yorku.zoom.us/j/96087161597