# Set Theory Talks

Global set theory seminar and conference announcements

## Event Tuesday, September 21

Carnegie Mellon Logic Seminar
TUESDAY, September 21, 2021 Set Theory Reading Group: 4:30 P.M., Online, Allison Wang, Carnegie Mellon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Hyperfiniteness and Ramsey notions of largeness ABSTRACT: The lowest non-trivial complexity class in the theory of Countable Borel Equivalence Relations (CBERs) is the class of hyperfinite CBERs. One difficulty that arises in studying this class is determining which CBERs are hyperfinite. Measure theory can be used to answer this question, but not many techniques can. For instance, a Baire category approach cannot distinguish hyperfinite CBERS: a result of Hjorth and Kechris states that every CBER on a Polish space is hyperfinite when restricted to some comeager set. We will discuss a classical proof of Mathias's theorem that every CBER on the Ellentuck Ramsey space is hyperfinite when restricted to some pure Ellentuck cube. Mathias's theorem implies that a Ramsey-theoretic approach also cannot distinguish hyperfinite CBERs. This is joint work with Aristotelis Panagiotopoulos. ORGANIZER'S NOTE: The talk will start after some socializing, at around 4:40 or 4:45.

## Wednesday seminar

Prague Set Theory Seminar
Dear all, We will restart the Wednesday seminar again this autumn. Hopefully we will not need pause it because of the pandemic again. The seminar should meet at the usual time and place, starting on Wednesday September 29. Please let me know in case you would know any email addresses I should add to the mailing list, or in case you would like to be removed from the list. The seminar meets on Wednesday September 29th at 11:00 in the Institute of Mathematics CAS, Zitna 25, seminar room, 3rd floor, front building. Program: Chris Lambie Hanson -- Strongly unbounded functions and productivity of chain conditions We discuss the existence of strongly unbounded functions on pairs of ordinals, which provide strong counterexamples to generalizations of Ramsey's theorem to uncountable cardinals. The talk will include a brief, gentle introduction to Todorcevic's powerful technique of walks on ordinals and an application to the infinite productivity of the $\kappa$-Knaster property. Some of the results are joint work with Assaf Rinot. Best, David

## Logic Seminar Wed 15 Sept 2021 16:00 hrs at NUS by Bakhadyr Khoussainov

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 15 September 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Bakhadyr Khoussainov, UESTC, Chengdu and The University of Auckland Title: Probability Structures URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: This talk belongs to the area of probabilistic logic semantics. The first contribution of this work is the introduction of probability structures. Probability structures are the algebraic structures equipped with probability functions on the domains and the atomic predicates. These structures extend type 1 probability structures introduced by Halpern and Bacchus. Type 1 probability structures contain probability functions on domains only. Our probability structures possess an additional statistical knowledge, - probability functions on atomic predicates. We present a method that builds probability spaces for the first order logic formulas and prove that our semantics is sound. The second contribution of this work is the introduction of smooth probability structures. The smooth probability structures carefully refine probability structures so that we have a better control of the probability spaces defined by first order logic formulas. For these structures we initiate the study of first order probability logic (FOPLS), investigate axiomatizability of FOPLS, and address decidability and undecidability questions of the sets of valid formulas. We also study a few algorithmic questions on probability structures.

## Logic Seminar Today 16:00 hrs SGT at NUS by Khoussainov and Stephan

NUS Logic Seminar
Hello, the password of this reminder was wrong, here the amended version. Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 8 September 2021, 16:00 hrs, Singapore Time Zone (GMT+8 hrs) Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Bakhadyr Khoussainov and Frank Stephan Title: Parity Games - Background and Algorithms. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Parity games are games where a marker is moved on a finite graph and each node is annotated with a natural number; the game runs forever and the largest number in an infinitely often visited node decides the winner, if it is even then player Anke wins else player Boris wins. Marcin Jurdzinski showed that this game is in UP intersected coUP and also provided the first not fully exponential algorithm for it; however, the exact time complexity remained unresolved. In 2017, Calude, Jain, Khoussainov, Li and Stephan found a quasipolynomial time algorithm which Jurdzinski and Lazic as well as Fearnley, Jain, Schewe, Stephan and Wojtczak improved the algorithm to be in polynomial space as well as quasipolynomial time. The talk provides the way this algorithm was found and the implications it has for the fixed-parameter-tracktability of parity games and related problems like coloured Muller games. Though now quite a number of quasipolynomial time algorithms are known and there is quite extensive research in this topic, the question on whether parity games can even be solved in polynomial time is still unresolved. This talk is given by Bakhadyr Khoussainov and Frank Stephan jointly also on behalf of their coauthors Cristian Calude, Sanjay Jain and Wei Li.

## Logic Seminar Today 16:00 hrs SGT at NUS by Khoussainov and Stephan

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 8 September 2021, 16:00 hrs, Singapore Time Zone (GMT+8 hrs) Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=3DUWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=3Dx3+y3 Speaker: Bakhadyr Khoussainov and Frank Stephan Title: Parity Games - Background and Algorithms. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Parity games are games where a marker is moved on a finite graph and each node is annotated with a natural number; the game runs forever and the largest number in an infinitely often visited node decides the winner, if it is even then player Anke wins else player Boris wins. Marcin Jurdzinski showed that this game is in UP intersected coUP and also provided the first not fully exponential algorithm for it; however, the exact time complexity remained unresolved. In 2017, Calude, Jain, Khoussainov, Li and Stephan found a quasipolynomial time algorithm which Jurdzinski and Lazic as well as Fearnley, Jain, Schewe, Stephan and Wojtczak improved the algorithm to be in polynomial space as well as quasipolynomial time. The talk provides the way this algorithm was found and the implications it has for the fixed-parameter-tracktability of parity games and related problems like coloured Muller games. Though now quite a number of quasipolynomial time algorithms are known and there is quite extensive research in this topic, the question on whether parity games can even be solved in polynomial time is still unresolved. This talk is given by Bakhadyr Khoussainov and Frank Stephan jointly also on behalf of their coauthors Cristian Calude, Sanjay Jain and Wei Li.

## Logic Seminar 8 September 2021 16:00 hrs at NUS by Bakhadyr Khoussainov and Frank Stephan

NUS Logic Seminar
Hello, there is a typing error in the below email. It should be "8 September 2021", so Wednesday next week. Frank Stephan On Thu, Sep 02, 2021 at 11:18:49PM +0800, Frank STEPHAN wrote: > Invitation to the Logic Seminar at the National University of Singapore > > Date: Wednesday, CORRECTED TO 08 Sep 2021, 16:00 hrs > > Talk via Zoom: > https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 > Meeting ID: 830 4925 8042 > Passcode: 1729=x3+y3 > > Speaker: Bakhadyr Khoussainov and Frank Stephan > > Title: Parity Games - Background and Algorithms. > > URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html > > Abstract: > Parity games are games where a marker is moved on > a finite graph and each node is annotated with a > natural number; the game runs forever and the largest > number in an infinitely often visited node decides > the winner, if it is even then player Anke wins > else player Boris wins. Marcin Jurdzinski showed > that this game is in UP intersected coUP and also > provided the first not fully exponential algorithm > for it; however, the exact time complexity remained > unresolved. In 2017, Calude, Jain, Khoussainov, Li > and Stephan found a quasipolynomial time algorithm > which Jurdzinski and Lazic as well as Schewe and his > collaborators improved to be in polynomial space > as well. The talk provides the way this algorithm > was found and the implications it has for the > fixed-parameter-tracktability of parity games and > related problems like coloured Muller games. Though > now quite a number of quasipolynomial time algorithms > are known and there is quite extensive research in this > topic, the question on whether parity games can even > be solved in polynomial time is still unresolved. > > This talk is given by Bakhadyr Khoussainov and > Frank Stephan jointly also on behalf of their coauthors > Cristian Calude, Sanjay Jain and Wei Li. >

## Logic Seminar 8 September 2021 16:00 hrs at NUS by Bakhadyr Khoussainov and Frank Stephan

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 11 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Bakhadyr Khoussainov and Frank Stephan Title: Parity Games - Background and Algorithms. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Parity games are games where a marker is moved on a finite graph and each node is annotated with a natural number; the game runs forever and the largest number in an infinitely often visited node decides the winner, if it is even then player Anke wins else player Boris wins. Marcin Jurdzinski showed that this game is in UP intersected coUP and also provided the first not fully exponential algorithm for it; however, the exact time complexity remained unresolved. In 2017, Calude, Jain, Khoussainov, Li and Stephan found a quasipolynomial time algorithm which Jurdzinski and Lazic as well as Schewe and his collaborators improved to be in polynomial space as well. The talk provides the way this algorithm was found and the implications it has for the fixed-parameter-tracktability of parity games and related problems like coloured Muller games. Though now quite a number of quasipolynomial time algorithms are known and there is quite extensive research in this topic, the question on whether parity games can even be solved in polynomial time is still unresolved. This talk is given by Bakhadyr Khoussainov and Frank Stephan jointly also on behalf of their coauthors Cristian Calude, Sanjay Jain and Wei Li.

## Logic Seminar today 16:00 hrs at NUS by Rupert Hoelzl, University of the Bundeswehr in Munich

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 1 September 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Rupert Hoelzl Title: The reverse mathematics of inductive inference URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: We investigates inductive inference from the perspective of reverse mathematics. Reverse mathematics is a framework that allows gauging the proof strength of theorems and axioms in many areas of mathematics. We apply its methods to basic notions of algorithmic learning theory such as Angluin's tell-tale criterion and its variants for learning in the limit and for conservative learning, as well as to the more general scenario of partial learning. These notions are studied in the reverse mathematics context for uniformly and weakly represented families of languages. The results are stated in terms of axioms referring to induction strength and to domination of weakly represented families of functions.

## Free Registration for IPEC 2021 until 29 August 2021 (Online Conference)

NUS Logic Seminar
Hello, Most likely on 8 September 2021, Bakhadyr Khoussainov and Frank Stephan will give an invited talk about the paper Deciding parity games in quasipolynomial time by Cristian Calude, Sanjay Jain, Bakhadyr Khoussainov, Wei Li and Frank Stephan from STOC 2017 and SIAM Journal on Computing at IPEC 2021. You can up to tomorrow (29 August 2021) register for free at this online occurring conference through the webpage http://algo2021.tecnico.ulisboa.pt/index.html#registration and information on the conference IPEC is on http://algo2021.tecnico.ulisboa.pt/IPEC2021/index.html The exact programme is not yet there, but will most likely be made available after tomorrow's free registration deadline for nonpresenting participants. IPEC is an International Symposium on Parameterised and Exact Computation. Sorry for the short notice, I was waiting for info about the conference going onto the webpage before sending this. Best regards, Frank

## Felix Weilacher on Tuesday (8/31) 3:30 PM Eastern

Carnegie Mellon Logic Seminar
TUESDAY, August 31 2021 Mathematical logic seminar: 3:30 P.M., Online, Felix Weilacher, Carnegie Mellon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Borel Edge Colorings for Finite Dimensional Groups ABSTRACT: In Borel graph combinatorics, one often produces a structure (e.g. a coloring) by dividing a graph into subgraphs with finite connected components, then defining the structure on those components via some straightforward uniformization result. We first give an overview of some recent work formalizing these notions and applying them to various problems. We then present our own application to the problem of edge coloring. For Borel actions of certain groups, we find "degree plus one" Borel edge colorings, matching the classical bound of Vizing. Furthermore, for finitely generated abelian groups, we are able to exactly determine Borel edge chromatic numbers.

## Logic Seminar 1 Sept 2021 16:00 hrs at NUS by Rupert Hoelzl, Univ. of the Bundeswehr, Munich

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 1 September 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Rupert Hoelzl Title: The reverse mathematics of inductive inference URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html We investigates inductive inference from the perspective of reverse mathematics. Reverse mathematics is a framework that allows gauging the proof strength of theorems and axioms in many areas of mathematics. We apply its methods to basic notions of algorithmic learning theory such as Angluin's tell-tale criterion and its variants for learning in the limit and for conservative learning, as well as to the more general scenario of partial learning. These notions are studied in the reverse mathematics context for uniformly and weakly represented families of languages. The results are stated in terms of axioms referring to induction strength and to domination of weakly represented families of functions.

## Logic Seminar 25 April 2021 16:00 hrs by Ng Keng Meng (NTU) at NUS (today)

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 25 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Ng Keng Meng Title: Are the rationals dense Abstract: There has been a recent revival in the interest in sub-computable mathematics. One of these approaches is to consider primitive recursive'' or punctual structures. This has led to a greater understanding in the effective content of well-known objects and proofs in classical computability theory. When considering the punctual anaologies of classical computabilitiy we often obtain strange and surprising results. I will discuss some recent work in progress in this area, focussing particularly on structural results. URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html

## RIMS Set Theory Workshop: October 12-15, 2021

Conference
RIMS SET THEORY WORKSHOP 2021 Announcement / Call for Contributions RIMS workshop "Recent Developments in Set Theory of the Reals" Date: Tuesday, October 12, 2021 to Friday, October 15, 2021 Venue: ONLINE (via ZOOM meeting), based on Japan Standard Time 9am--5pm Contact: Masaru Kada (Osaka Prefecture University) / kada@mi.s.osakafu-u.ac.jp Workshop Overview: This online workshop, hosted by RIMS (Research Institute for Mathematical Sciences, Kyoto University), is mainly (but not only) focused on recent developments in set theory of the reals. The program will contain a minicourse (a series of lectures) as well as contributed talks. In the minicourse, we invite Joerg Brendle (Kobe University) and Diego Mejia (Shizuoka University), who will give us lectures on some forcing techniques (e.g., Boolean ultrapowers, submodel methods, etc.) and related results in set theory of the reals. We welcome every researcher in set theory or related research fields. Please join us! Registration: Please submit a registration form to register your participation / contributed talk, from the following URL: https://forms.gle/1156YFMp1bN9GEDJ9 Deadline for contributed talks: September 9, 2021 Deadline for participation: October 10, 2021

## First math logic seminar of the new semester

Carnegie Mellon Logic Seminar
TUESDAY, August 31 2021 Mathematical logic seminar: 3:30 P.M., Online, Felix Weilacher, Carnegie Mellon University Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Borel Edge Colorings for Finite Dimensional Groups ABSTRACT: In Borel graph combinatorics, one often produces a structure (e.g. a coloring) by dividing a graph into subgraphs with finite connected components, then defining the structure on those components via some straightforward uniformization result. We first give an overview of some recent work formalizing these notions and applying them to various problems. We then present our own application to the problem of edge coloring. For Borel actions of certain groups, we find "degree plus one" Borel edge colorings, matching the classical bound of Vizing. Furthermore, for finitely generated abelian groups, we are able to exactly determine Borel edge chromatic numbers.

## Logic Seminar at NUS on Wed 18 Aug 2021 at 16:00 hrs

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 18 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Yu Liang, Nanjing University Title: Generalizing Besicovitch-Davis theorem URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Besicovitch-Davis theorem says that the Hausdorff dimension of every analytic set can be approximated by its closed subset. But the Besicovitch-Davis theorem fails for co-analytic sets under the assumption V=L as observed by Slaman. We prove that the theorem holds for arbitrary sets under ZF+sTD. We also prove that the theorem holds for Sigma-1-2-sets under Martin's axiom. This is joint work with Peng Yinhe and Wu Liuzhen.

## Logic Seminar 11 Aug 2021 16:00 hrs at NUS by Frank Stephan

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 11 August 2021, 16:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/83049258042?pwd=UWViaWNvTFUrdFdhOHJCdEVydnVkdz09 Meeting ID: 830 4925 8042 Passcode: 1729=x3+y3 Speaker: Frank Stephan Title: A survey on the structures realised by positive equivalence relations URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Let a positive equivalence relation to be an r.e. equivalence relation on the set of natural numbers with infinitely many equivalence relations. Khoussainov initiated with coauthors a deep study of the following question: Given a positive equivalence relation eta, which structures from a given set of structures does this equivalence relation realise? Here realisation means that functions in the structure are recursive and relations are r.e. with the equality itself given by the equivalence relation eta. In other words, the given r.e. structure divided by eta is the structure realised by eta. Now questions studied by Khoussainov and his coworkers included questions like "What is the partial ordering on positive equivalence relations eta,rho where eta is below rho iff every structure of the given type realised by eta is also realised by rho? Besides algebraic structures and orders, it has also been studied how the learnability notions behave with respect to uniformly r.e. one-one families realised by positive equivalence relations.

## Events next Tuesday

Carnegie Mellon Logic Seminar
TUESDAY, August 10 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 6) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic. TUESDAY, August 10, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 7) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## Events next Tuesday

Carnegie Mellon Logic Seminar

## Logic seminar and set theory reading group for next week

Carnegie Mellon Logic Seminar
ORGANIZERS' NOTE: Last week, these seminars were postponed until next week due to last minute technical issues. -------------------------------------------------------------------------- TUESDAY, July 27, 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 2) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic. TUESDAY, July 27, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Zoom link: https://cmu.zoom.us/j/621951121?pwd=eWEwVit5WUxlUExOWE51ajdFZnJ2Zz09 Meeting ID: 621 951 121 Passcode: 617076 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 3) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## An apology to all about today's seminar

Toronto Set Theory Seminar
Hello everyone,

As some of you noticed, today there was no seminar although it was announced and not cancelled. We are very sorry about this miscommunication on our end.

Also, I offer an apology to everyone for not being in the meeting to explain the situation.

Last minute yesterday, we found out that the speaker was not going to be able to assist. I was supposed to send an email cancelling the seminar today, but I didn't.

Today I got my first vaccine shot so my mind was elsewhere (along with my internet and my computer), so I was not able to warn everyone about the cancellation.

Again, we offer an apology. This speaker will be able to participate in the seminar in september. In the meanwhile, we do not have seminar next week.

I thank everyone for your comprehension.

Best regards

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk tomorrow by Gianluca Paolini at 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:Gianluca Paolini
Date and Time: Friday, July 23rd, 2021 - 1:30pm to 3:00pm
Title: Torsion-Free Abelian Groups are Borel Complete
Abstract:
We prove that the Borel space of torsion-free Abelian groups with domain is Borel complete, i.e., the isomorphism relation on this Borel space is as complicated as possible, as an isomorphism relation. This solves a long-standing open problem in descriptive set theory, which dates back to the seminal paper on Borel reducibility of Friedman and Stanley from 1989.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk Friday 23rd June by Gianluca Paolini at 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:Gianluca Paolini
Date and Time: Friday, July 23rd, 2021 - 1:30pm to 3:00pm
Title: Torsion-Free Abelian Groups are Borel Complete
Abstract:
We prove that the Borel space of torsion-free Abelian groups with domain is Borel complete, i.e., the isomorphism relation on this Borel space is as complicated as possible, as an isomorphism relation. This solves a long-standing open problem in descriptive set theory, which dates back to the seminal paper on Borel reducibility of Friedman and Stanley from 1989.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk in ONE hour by Richard Matthews

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Richard Matthews
Date and Time: Friday, July 16th, 2021 - 1:30pm to 3:00pm
Title: Large Cardinals in Weakened Axiomatic Theories
Abstract:
The Kunen Inconsistency is an important milestone in the study of axiomatic set theory, placing a hard limit on how close the target model of a non-trivial elementary embedding can be to the full universe. In particular, it shows that the existence of a Reinhardt embedding, that is a non-trivial embedding of the full universe into itself, is inconsistent. It is well-known that all proofs we currently have rely extensively on the fact that we are working with the full power of ZFC, most notably the essential use of choice.

In this talk we shall discuss the notion of a Reinhardt embedding over several weakened base theories, primarily ZFC without Power Set, Zermelo and Power Kripke Platek. We shall see how to obtain some upper bounds, lower bounds and equiconsistency results in terms of the usual ZFC large cardinal hierarchy as well as many unexpected characteristics such embeddings can have. Moreover, we shall see that, under reasonable additional assumptions, it is possible to reobtain Kunen-type inconsistency results in both ZFC without Power Set and Power Kripke Platek plus Well-Ordering.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Events next Tuesday

Carnegie Mellon Logic Seminar
TUESDAY, July 20, 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 2) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic. TUESDAY, July 20, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 3) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## Today at 1 30 pm talk by Richard Matthews (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Richard Matthews
Date and Time: Friday, July 16th, 2021 - 1:30pm to 3:00pm
Title: Large Cardinals in Weakened Axiomatic Theories
Abstract:
The Kunen Inconsistency is an important milestone in the study of axiomatic set theory, placing a hard limit on how close the target model of a non-trivial elementary embedding can be to the full universe. In particular, it shows that the existence of a Reinhardt embedding, that is a non-trivial embedding of the full universe into itself, is inconsistent. It is well-known that all proofs we currently have rely extensively on the fact that we are working with the full power of ZFC, most notably the essential use of choice.

In this talk we shall discuss the notion of a Reinhardt embedding over several weakened base theories, primarily ZFC without Power Set, Zermelo and Power Kripke Platek. We shall see how to obtain some upper bounds, lower bounds and equiconsistency results in terms of the usual ZFC large cardinal hierarchy as well as many unexpected characteristics such embeddings can have. Moreover, we shall see that, under reasonable additional assumptions, it is possible to reobtain Kunen-type inconsistency results in both ZFC without Power Set and Power Kripke Platek plus Well-Ordering.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Two events on Tuesday

Carnegie Mellon Logic Seminar
TUESDAY, July 13, 2021 Mathematical logic seminar: 3:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: An introduction to strong homology ABSTRACT: We will introduce strong homology, which aims to correct the failures of Čech homology, particularly the failure of exactness. TUESDAY, July 13, 2021 Set Theory Reading Group: 4:30 P.M., Online, Nathaniel Bannister, Carnegie Mellon University (beginning Fall, 2021) Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Additivity of strong homology for locally compact separable metric spaces (part 1) ABSTRACT: This series of talks will cover the 2019 paper "On the additivity of strong homology for locally compact separable metric spaces" as well as recent work establishing a conceptual basis for the results therein. We will show that (relative to a weakly compact cardinal) it is consistent for strong homology to be additive and compactly supported on the class of locally compact separable metric spaces. In the process, we develop an equivalent algebraic statement and a sufficient cardinal-theoretic condition. This is joint work with Justin Moore, Jeffrey Bergfalk, and Stevo Todorcevic.

## Talk Tomorrow by Osvaldo Guzmán 1 30 pm (Totonto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance. See attached image or follow the link below.

Here the speaker information:

Speaker:  Osvaldo Guzmán González
Date and Time: Friday, July 9th, 2021 - 1:30pm to 3:00pm
Title: MAD families and strategically bounding forcings
Abstract:
The notion of strategically bounding forcings is a natural game-theoretic
strengthening of the bounding property for partial orders.  In this talk, we
will study the basic properties of strategically bounding forcings and talk
about indestructibility of MAD families. The motivation for this work is the
problem of Roitman. I will talk about results that were obtained with
Michael Hrusak, Joerg Brendle and Dilip Raghavan.
Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Series finale

Carnegie Mellon Logic Seminar
TUESDAY, July 6, 2021 Mathematical logic seminar: 3:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 7 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module). TUESDAY, July 6, 2021 Set Theory Reading Group: 4:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 8 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

## Talk this Friday (July 9th) by Osvaldo Guzmán 1 30 pm (Totonto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

TBD

Here the speaker information:

Speaker:  Osvaldo Guzmán González
Date and Time: Friday, July 9th, 2021 - 1:30pm to 3:00pm
Title: MAD families and strategically bounding forcings
Abstract:
The notion of strategically bounding forcings is a natural game-theoretic
strengthening of the bounding property for partial orders.  In this talk, we
will study the basic properties of strategically bounding forcings and talk
about indestructibility of MAD families. The motivation for this work is the
problem of Roitman. I will talk about results that were obtained with
Michael Hrusak, Joerg Brendle and Dilip Raghavan.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## James Cummings series continues

Carnegie Mellon Logic Seminar
TUESDAY, June 29, 2021 Mathematical logic seminar:  3:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 5 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module). TUESDAY, June 29, 2021 Set Theory Reading Group:  4:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Homological algebra for logicians ABSTRACT: This is part 6 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

## Talk TODAY by Riley Thornton 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:   Riley Thornton
Date and Time: Friday, June 25th, 2021 - 1:30pm to 3:00pm
Title: Effectivization in Borel Combinatorics
Abstract:
In Borel combinatorics, we often want to know when a Borel graph (or equivalence relation, quasi-order, etc) admits a Borel witness to some combinatorial property, . An effectivization theorem for says that any (lightface) graph with a Borel witness to in fact has a witness. This kind of effectivization gives a strong upper bound on the projective complexity of the set of graphs where a definable witness exists and suggests that such graphs might admit a nice structural characterization. This talk will present a streamlined method for proving effectivization theorems, give a number of applications, and discuss some related dichotomy theorems.

Please visit http://www.fields.utoronto.ca/talks/Effectivization-Borel-Combinatorics for a cleaner version of the abstract.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk this Friday 25th (in less than two days) by Riley Thornton 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:   Riley Thornton
Date and Time: Friday, June 25th, 2021 - 1:30pm to 3:00pm
Title: Effectivization in Borel Combinatorics
Abstract:
In Borel combinatorics, we often want to know when a Borel graph (or equivalence relation, quasi-order, etc) admits a Borel witness to some combinatorial property, . An effectivization theorem for says that any (lightface) graph with a Borel witness to in fact has a witness. This kind of effectivization gives a strong upper bound on the projective complexity of the set of graphs where a definable witness exists and suggests that such graphs might admit a nice structural characterization. This talk will present a streamlined method for proving effectivization theorems, give a number of applications, and discuss some related dichotomy theorems.

Please visit http://www.fields.utoronto.ca/talks/Effectivization-Borel-Combinatorics for a cleaner version of the abstract.

I'll send the next reminder in the morning of the day of the talk

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk on Thursday, June 24

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, June 24 "Preserving levels of projective determinacy and regularity properties" Johannes Schürz (TU Wien) Since \mathbf{\Pi}^1_1-determinacy is a desirable property on the reals, the natural question arises as to how one can preserve it under forcing. We will show using the technique of capturing that the statement 'Every real has a sharp' is preserved under any countable support iteration of 'simply' definable forcing notions. By the famous results of L. Harrington and D. Martin this shows that \mathbf{\Pi}^1_1-determinacy is preserved under such iterations. More generally, our theorem also shows that the statement 'M_n^\sharp(x) exists for every real x \in \omega^\omega' is preserved. By the results of I. Neeman and H. Woodin this generalizes our result to higher levels of projective determinacy. Without the existence of large cardinals the technique of capturing can still be used to show preservation results for regularity properties such as the \mathbf{\Delta}^1_2- or \mathbf{\Sigma}^1_2-Baire property. This is a joint project with J. Schilhan and P. Schlicht. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## Talk tomorrow 18th by David Schrittesser (1:30 pm to 3pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:  David Schrittesser
Date and Time: Friday, June 18th, 2021 - 1:30pm to 3:00pm
Title:  A taste of nonstandard analysis and statistical decision theory
Abstract:
Statistical decision theory takes inspiration from game theory to
provide a basic framework in which one can reason about optimality (or
lack thereof) of statistical methods, such as estimators and tests.
One (very weak) property of such methods is admissibility - roughly, a
method of estimation is admissible if there is no other which does
better under all circumstances (in a sense specified by the decision
theoretical framework).

Although a weak property, admissibility is notoriously hard to
characterize. Recently we have found a characterization of admissibility
(in a large class of statistical problems) in Bayesian terms, by using
prior probability distributions which can take on infinitesimal values.

(The talk will not presuppose any knowledge on statistics or nonstandard
analysis. Joint work with D. Roy and H. Duanmu.)
Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk this Friday 18th by David Schrittesser (1:30 pm to 3pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker:  David Schrittesser
Date and Time: Friday, June 18th, 2021 - 1:30pm to 3:00pm
Title:  A taste of nonstandard analysis and statistical decision theory
Abstract:
Statistical decision theory takes inspiration from game theory to
provide a basic framework in which one can reason about optimality (or
lack thereof) of statistical methods, such as estimators and tests.
One (very weak) property of such methods is admissibility - roughly, a
method of estimation is admissible if there is no other which does
better under all circumstances (in a sense specified by the decision
theoretical framework).

Although a weak property, admissibility is notoriously hard to
characterize. Recently we have found a characterization of admissibility
(in a large class of statistical problems) in Bayesian terms, by using
prior probability distributions which can take on infinitesimal values.

(The talk will not presuppose any knowledge on statistics or nonstandard
analysis. Joint work with D. Roy and H. Duanmu.)

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk and master defense Michael Zechner

Kurt Godel Research Center

## Reminder: Boise Extravaganza in Set Theory, June 17-19

Conference
This post is an update regarding BEST, which begins next Thursday, 17 June and runs through 17 June. We are looking forward to seeing you! You can find the list of speakers and talk titles below. The latest information will always be available on the website. BEST website: https://www.boisestate.edu/math/best/ Zoom ID 92626476913 (https://boisestate.zoom.us/j/92626476913) Plenary speakers David Fernández Bretón (UNAM). Hindman’s theorem as a weak version of the Axiom of Choice Victoria Gitman (CUNY). Characterizing large cardinals via abstract logics Jun Le Goh (Wisconsin). Inseparable pairs and recursion theory Lynne Yengulalp (Wake Forest). Completeness, G-deltas, and games Joseph Zielinski (North Texas). Orbit equivalence relations of some classes of non-locally compact Polish groups Additional speakers Filippo Calderoni (UIC). Rotation equivalence and cocycle superrigidity for compact actions Natasha Dobrinen (Denver). Big Ramsey degrees of universal inverse limit structures Thomas Gilton (Pittsburgh). Club stationary reflection and the special Aronszajn tree property Osvaldo Guzmán González (UNAM). MAD families and strategically bounding forcings Randall Holmes (Boise). An outline of a proof of the consistency of New Foundations Martina Iannella (Udine). The complexity of convex bi-embeddability among countable linear orders Krzysztof Kowitz (Gdańsk). Differentially compact space and Hindman space Maxwell Levine (Freiburg). Patterns of stationary reflection Renan Mezabarba (UFES). A characterization of productive cellularity Aristotelis Panagiotopoulos (Münster). Dynamical obstructions to classification by (co)homology and other TSI-group invariants Nick Ramsey (UCLA). Exact saturation in pseudo-elementary classes Panagiotis Rouvelas (Patras). Models of predicative NF Cory Switzer (KGRC). Tight eventually different families Riley Thornton (UCLA). Effectivization in Borel combinatorics Kameryn Williams (Hawaii). Coding sets into inner mantles Jenna Zomback (UIUC). Ergodic theorems along trees
View attachments

## CMU logic events during coming week

Carnegie Mellon Logic Seminar

TUESDAY, June 15, 2021

Mathematical logic seminar:  3:30 P.M., Online, James Cummings, Carnegie Mellon University

Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us]
Meeting ID: 621 951 121

TITLE: Homological algebra for logicians

ABSTRACT: This is part 3 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology.

I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

TUESDAY, June 15, 2021

Set Theory Reading Group:  4:30 P.M., Online, James Cummings, Carnegie Mellon University

Join Zoom Meeting: https://cmu.zoom.us/j/621951121  [cmu.zoom.us]
Meeting ID: 621 951 121

TITLE: Homological algebra for logicians

ABSTRACT: This is part 4 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology.

I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module).

THURSDAY, June 17, 2021

Ph.D. Thesis Defense:  12:00 P.M., Online, Marcos Mazari-Armida

Zoom:
https://cmu.zoom.us/j/96301869290?pwd=Qk1zS0h6ZThmUnRpbmNLNkVJSjkrQT09

TITLE OF DISSERTATION: Remarks on classification theory for abstract elementary classes with applications to abelian group theory and ring theory

EXAMINERS:
Prof. Rami Grossberg (Committee Chair)
Prof. John Baldwin, UIC
Prof. Will Boney, Texas State
Prof. James Cummings

## Barcelona Set theory Seminar

Barcelona Logic Seminar
Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Raffaella Cutolo (Università degli Studi di Napoli Federico II)
TITLE: N-Berkeley cardinals and the two futures of set theory
DATE: 9 June 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Talk tomorrow by Piotr Szewczak (1:30 pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Piotr Szewczak
Date and Time: Friday, June 4th, 2021 - 1:30pm to 3:00pm
Title: Abstract colorings, games and ultrafilters
Abstract:
During the talk we consider various kinds of Ramsey-type theorems.

Bergelson and Hindman investigated finite colorings of the complete graph [N]^2 with vertices in natural numbers, involving an algebraic structure of N. It follows from their result that for each finite coloring of [N]^2, there are finite pairwise disjoint sets F1, F2, … such that each set Fn contains an arithmetic progression of length n and all edges between vertices from different sets Fn have the same color. Colorings of graphs appear also in the context of combinatorial covering properties. Scheepers proved that a set of reals X is Menger if and only if for every finite coloring of the complete graph whose vertices are open sets in X and an open omega-cover U of X (i.e., every finite subset of X is contained in a proper subset of X from the cover), there are finite pairwise disjoint subfamilies F1, F2, … of U such that the union of these families is point-infinite cover of X and all edges between vertices from different sets Fn have the same color.

The aim of the talk is to present a theorem that captures many results in a similar spirit (including mentioned above). To this end we use topological games and some special ultrafilters in the Stone—Cech compactification of semigroups. The research was motivated by the recent result of Tsaban, who extended the celebrated Hindman Finite Sum Theorem (and its high-dimensional version due to Milliken and Taylor) to covers of Menger spaces.

Ivan Ongay Valverde
ongay@yorku.ca
York University Postdoc (he/his)

## Talk this Friday June 4th by Piotr Szewczak (1:30 pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Piotr Szewczak
Date and Time: Friday, June 4th, 2021 - 1:30pm to 3:00pm
Title:   Abstract colorings, games and ultrafilters
Abstract:
During the talk we consider various kinds of Ramsey-type theorems.

Bergelson and Hindman investigated finite colorings of the complete graph [N]^2 with vertices in natural numbers, involving an algebraic structure of N. It follows from their result that for each finite coloring of [N]^2, there are finite pairwise disjoint sets F1, F2, … such that each set Fn contains an arithmetic progression of length n and all edges between vertices from different sets Fn have the same color. Colorings of graphs appear also in the context of combinatorial covering properties. Scheepers proved that a set of reals X is Menger if and only if for every finite coloring of the complete graph whose vertices are open sets in X and an open omega-cover U of X (i.e., every finite subset of X is contained in a proper subset of X from the cover), there are finite pairwise disjoint subfamilies F1, F2, … of U such that the union of these families is point-infinite cover of X and all edges between vertices from different sets Fn have the same color.

The aim of the talk is to present a theorem that captures many results in a similar spirit (including mentioned above). To this end we use topological games and some special ultrafilters in the Stone—Cech compactification of semigroups. The research was motivated by the recent result of Tsaban, who extended the celebrated Hindman Finite Sum Theorem (and its high-dimensional version due to Milliken and Taylor) to covers of Menger spaces.

Ivan Ongay Valverde
ongay@yorku.ca
York University Postdoc (he/his)

## Barcelona Set theory Seminar

Barcelona Logic Seminar
Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Michał Tomasz Godziszewski  (University of Warsaw)
TITLE: The Multiverse, Recursive Saturation and Well-Foundedness Mirage
DATE: 2 June 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Two events on June 8

Carnegie Mellon Logic Seminar
TUESDAY, June 8, 2021 Mathematical logic seminar: 3:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Title: Homological algebra for logicians ABSTRACT: This is part 1 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module) TUESDAY, June 8, 2021 Set Theory Reading Group: 4:30 P.M., Online, James Cummings, Carnegie Mellon University Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Title: Homological algebra for logicians ABSTRACT: This is part 2 of a short series of talks aimed at giving some background for Nathaniel Bannister's forthcoming seminars. Nathaniel's talks will describe his work with Bergfalk and Moore on the additivity of strong homology. I will give a rapid overview of some necessary background in homological algebra (eg abelian categories, chain complexes, derived functors). I will assume very little background, just familiarity with basic notions in category theory (category, functor, natural transformation) and algebra (the definition of an R-module)

## Talk Tomorrow by Boban Velickovic at 1 30 (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Boban Velickovic
Date and Time: Friday, May 28th, 2021 - 1:30pm to 3:00pm
Title:   Non vanishing higher derived limits
Abstract:
In the study of strong homology Mardesic and Prasolov isolated a certain inverse system of abelian groups A indexed by functions from \omega to \omega.
They showed that if strong homology is additive on a class of spaces containing closed subsets of Euclidean spaces then the higher derived limits lim^n A must vanish for n >0.
They also proved that under the Continuum Hypothesis lim^1 A does not vanish. On the other hand Down, Simon and Vaughan showed that under PFA lim^1 A=0
The question whether lim^n A vanishes higher n has attracted considerable attention recently. First, Bergfalk shows that it was consistent lim^2 A does not vanish.
Later Bergfalk and Lambie-Hanson showed that, assuming modest large cardinal axioms, lim^n A vanishes for all n. The large cardinal assumption was later removed by Bergfalk, Hrusak and Lambie-Hanson. We complete the picture by showing that, for any n>0, it is relatively consistent with ZFC that lim^n A is non zero.

This is joint work with Alessandro Vignati.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk on Thursday, May 27

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, May 27 "Independent families and singular cardinals" Diana Carolina Montoya (KGRC) In this talk, we will discuss the concept of independent families for uncountable cardinals. First, we will mention a summary of results regarding the existence of such families in the case of an uncountable regular cardinal. In the second part, we focus on the singular case and present two results of ours. This is joint work with Omer Ben-Neria. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at! Please note: There will be no talk in the research seminar next Thursday, June 3 (Corpus Christi).

## An interesting series of talks for grad students

Toronto Set Theory Seminar
Hello everyone,

Vera Fischer is organizing a series of short talks intended for graduate students.
The idea of the talks is one short talk once a week, with the idea to
introduce some areas of set theory to the students.

Interested students should just send Vera a short email and she will add
them to the list of participants.   vera.fischer@univie.ac.at

The time is not optimal for people in the american continent time zones
(it is 9:30am CET, Fridays, May 28-June 18), but she will record the
talks for those who want to hear them at a later point. Here is
the program until the end of the semester.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk Friday May 27th (this friday) by Boban Velickovic at 1 30 (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Boban Velickovic
Date and Time: Friday, May 28th, 2021 - 1:30pm to 3:00pm
Title:   Non vanishing higher derived limits
Abstract:
In the study of strong homology Mardesic and Prasolov isolated a certain inverse system of abelian groups A indexed by functions from \omega to \omega.
They showed that if strong homology is additive on a class of spaces containing closed subsets of Euclidean spaces then the higher derived limits lim^n A must vanish for n >0.
They also proved that under the Continuum Hypothesis lim^1 A does not vanish. On the other hand Down, Simon and Vaughan showed that under PFA lim^1 A=0
The question whether lim^n A vanishes higher n has attracted considerable attention recently. First, Bergfalk shows that it was consistent lim^2 A does not vanish.
Later Bergfalk and Lambie-Hanson showed that, assuming modest large cardinal axioms, lim^n A vanishes for all n. The large cardinal assumption was later removed by Bergfalk, Hrusak and Lambie-Hanson. We complete the picture by showing that, for any n>0, it is relatively consistent with ZFC that lim^n A is non zero.

This is joint work with Alessandro Vignati.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   David Asperó (UEA, Norwich)
TITLE: Around (*)
DATE: 26 May 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   David Asperó (UEA, Norwich)
TITLE: Around (*)
DATE: 26 May 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   David Asperó (UEA, Norwich)
TITLE: Around (*)
DATE: 26 May 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## (KGRC) research seminar talk on Thursday, May 20

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, May 20 "Extensions of inner models of ZFC" Lev Bukovsky (Pavol Jozef Šafárik University in Košice, Slovakia) I would like to present some results of members of Vopěnka's seminary in 1960's and 1970's (B. Balcar, P. Vopěnka, P. Hájek and me), which were either not published or published in the language of semisets theory. Consequently, those results are not commonly known. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Luca Incurvati (Amsterdam)
TITLE: Iteration, dependence and structuralism
DATE: 19 May 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, May 3, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, May 3rd, 4.15-6.15 (NY time)
Title: Marsilius of Inghen, John Buridan and the Semantics of Impossibility

Abstract: In the 14th-century, imaginable yet in some sense impossible non-entities start playing a crucial role in logic, natural philosophy and metaphysics. Throughout the later middle ages and well into early modernity, Marsilius of Inghen’s name comes to be unavoidably associated with the semantics of imaginable impossibilities in most logical and metaphysical discussions. In this paper I analyse Marsilius of Inghen’s semantic treatment of impossible referents, through a comparison with John Buridan’s. While in many ways Marsilius is profoundly influenced by Buridan’s philosophy, his semantic analysis of impossibilia is radically different from Buridan’s. Overall, Buridan tends to analyse away impossible referents in terms of complex concepts by combining possible simple individual parts. Marsilius, on the one hand, treats impossibilia as imaginable referents that are properly unitary; on the other hand, he extends the scope of his modal semantics beyond the inclusion of merely relative impossibilities, allowing for a full semantic treatment of absolute impossibilities as well. Here, I will explore the extent of these differences between Buridan’s and Marsilius of Inghen’s semantics, their presuppositions, and their respective conceptual impact on early modern philosophy of logic and mathematics.

- - - - Tuesday, May 4, 2021 - - - -

- - - - Wednesday, May 5, 2021 - - - -

- - - - Thursday, May 6, 2021 - - - -

Philog Seminar
Thursday May 6, 2021, 6:30 PM
Nietzsche on, Logic, Philosophy, and Moral Values

Introduction: Studies in logic rarely ever mention Fredrich Nietzsche.  There is very little literature on Nietzsche’s critique of classical logic and there is no indication that he followed the developments that were occurring in the field in the 19th century by contemporaneous thinkers such as George Boole, Frege, or Augustus De Morgan.  Yet, logic is central to Nietzsche’s seminal work Beyond Good and Evil: Prelude to a Philosophy of the Future, henceforth referred to as BGE.  Believing that classical logic falsely reinforces the religious promise of absolutism and certainty, Nietzsche rejects the possibility of a priori truths qua truth, but embraces logic to the extent that he considers it the vehicle that systematically discharges a philosopher’s energy and morality onto the world.

In this talk I consider Nietzsche’s critique of moral values as they relate to his rejection of both a priori truths and the semantic principle of bivalence, or what he calls the “faith of opposite values”.  I argue that Nietzsche’s approach to philosophy, logic, and moral values heralds the future philosophical significance of multivalent systems and paraconsistent logic.

A Zoom link will be posted on  https://philog.arthurpaulpedersen.org/

- - - - Friday, May 7, 2021 - - - -

Set Theory Seminar
Friday, May 7, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Benjamin Goodman, CUNY
Woodin's Extender Algebra

This oral exam talk will present a proof of Woodin's result that every real number is generic over some iterated ultrapower of any model with a Woodin cardinal. No fine structure theory will be used, and there will be a brief introduction to iteration trees.

Next Week in Logic at CUNY:

- - - - Monday, May 10, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, May 10th, 4.15-6.15 (NY time)
Filippo Casati (Lehigh)

Title: Heidegger on the Limits and Possibilities of Human Thinking

Abstract: In my talk, I will address what Heidegger calls ‘the basic problem’ of his philosophy, that is, the alleged incompatibility between the notion of Being, our thinking, and logic. First of all, I will discuss some of the ways in which Heideggerians have dealt with this incompatibility by distinguishing what I call the irrationalist and rationalist interpretation. Secondly, I will argue that these two interpretations face both exegetical and philosophical problems. To conclude, I will defend an alternative way to address the incompatibility between the notion of Being, our thinking, and logic. I will argue that, in some of his late works, Heidegger seems to suggest that the real problem lies in the philosophical illusion that we can actually assess the limits of our thinking and, therewith, our logic. Heidegger’s philosophy, I deem, wants to free us from such a philosophical illusion by delivering an experience which reminds us that our thinking is something we can never ‘look at from above’ in order to either grasp its limits or realize that it has no limits whatsoever.

- - - - Tuesday, May 11, 2021 - - - -

- - - - Wednesday, May 12, 2021 - - - -

- - - - Thursday, May 13, 2021 - - - -

Philog Seminar
Thursday May 13, 2021, 6:30 PM

Eric Pacuit, University of Maryland

Epistemic Networks for Imprecise Agents

Abstract: What is the best form for social influence to take?  Are all policies which aim to increase the amount of interaction over a particular issue likely to be successful in their aims?  In this talk, I will survey some models that have been proposed by economists and social epistemologists to address these questions. These models typically assume that the agents have precise beliefs about the proposition that they are trying to learn.  However, in many learning situations, at least some of the agents may have imprecise beliefs about the proposition that they are trying to learn.  The second part of the talk will report on some work in progress with Paul Pedersen about how best to design communication networks when some agents have imprecise beliefs.

Eric Pacuit is an associate professor in the Department of Philosophy at the University of Maryland. Prior to coming to Maryland, Eric did his graduate work at the City University of New York Graduate Center, and was a postdoctoral researcher at the Institute for Logic, Language and Computation at the University of Amsterdam and in the Departments of Philosophy and Computer Science at Stanford University. Eric’s primary research interests are in logic (especially modal logic), game theory, social choice theory, and formal and social epistemology. His research has been funded by the Natural Science Foundation and a Vidi grant from the Dutch science foundation (NWO).

A Zoom link will be posted on https://philog.arthurpaulpedersen.org/ on Wednesday

- - - - Friday, May 14, 2021 - - - -

Set Theory Seminar
Friday, May 14, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Corey Switzer, University of Vienna
Tight Maximal Eventually Different Families

Maximal almost disjoint (MAD) families and their relatives have been an important area of combinatorial and descriptive set theory since at least the 60s. In this talk I will discuss some relatives of MAD families, focussing on eventually different families of functions f:ωωf:ω→ω and eventually different sets of permutations pS(ω)p∈S(ω). In the context of MAD families it has been fruitful to consider various strengthenings of the maximality condition to obtain several flavors of 'strongly' MAD families. One such strengthening that has proved useful in recent literature is that of tightness. Tight MAD families are Cohen indestructible and come with a properness preservation theorem making them nice to work with in iterated forcing contexts.

I will introduce a version of tightness for maximal eventually different families of functions f:ωωf:ω→ω and maximal eventually different families of permutations pS(ω)p∈S(ω) respectively. These tight eventually different families share a lot of the nice, forcing theoretic properties of tight MAD families. Using them, I will construct explicit witnesses to ae=ap=1ae=ap=ℵ1 in many known models of set theory where this equality was either not known or only known by less constructive means. Working over LL we can moreover have the witnesses be Π11Π11 which is optimal for objects of size 1ℵ1 in models where CHCH fails. These results simultaneously strengthen several known results on the existence of definable maximal sets of reals which are indestructible for various definable forcing notions. This is joint work with Vera Fischer.

Next Week in Logic at CUNY:

- - - - Monday, May 17, 2021 - - - -

- - - - Tuesday, May 18, 2021 - - - -

- - - - Wednesday, May 19, 2021 - - - -

- - - - Thursday, May 20, 2021 - - - -

- - - - Friday, May 21, 2021 - - - -

Set Theory Seminar
Friday, May 21, 1pm
The seminar will take place virtually at 1pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Omer Ben-Neria, Hebrew University
TBA

- - - - Other Logic News - - - -

- - - - Web Site - - - -

"Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)"

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Sakaé Fuchino (Kobe)
TITLE: Generically supercompact cardinals as reflection principles
DATE: 12 April 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## All links to today talk work (preferably, use the one to fill the form)

Toronto Set Theory Seminar
Hello everyone,

Our webmaster is a magician, so any of the links I have sent will lead to the seminar talk.

Nevertheless, since the fields institute like to have general data about who attends, the following link will be the one that will lead you to the registration form and then to the talk. This is the best one to use (that, curiously, is the same as in the very first email):

That is the link that you can also find in the webpage. Thanks to Miles for his quick and awesome help.

Best

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Today (Friday, 7th) talk by Itsvan Juhasz

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and, only in case that it appears, fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance. This is the correct link.

Here the speaker information:

Speaker: Itsvan Juhasz
Date and Time: Friday, May 7th, 2021 - 1:30pm to 3:00pm
Title:  Anti-Urysohn spaces
Abstract: please see attached pdf or visit http://www.fields.utoronto.ca/talks/Anti-Urysohn-spaces

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk Tomorrow by Itsvan Juhasz at 1 30 pm (Toronto time)

Toronto Set Theory Seminar
I owe an apology to everyone. Our recurring meeting ended without me noticing, for this session we will use the following link. Most likely the registration form will not appear.

I'll talk with the webmaster to fix all the issues.

Fields Seminars 1 is inviting you to a scheduled Zoom meeting.

Topic: Set Theory Seminar
Time: 1:30-3:00 pm Friday May 7th

Join Zoom Meeting
https://zoom.us/j/97109130026?pwd=a2VMVUJBMmZweXU4a0ZnaE02NmJvZz09

Meeting ID: 971 0913 0026
Passcode: 729463
One tap mobile

Meeting ID: 971 0913 0026

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

On Thu, May 6, 2021 at 7:00 PM Ivan Ongay Valverde <ivan.ongay.valverde@gmail.com> wrote:
Hello everyone,

Please use the following link and fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Itsvan Juhasz
Date and Time: Friday, May 7th, 2021 - 1:30pm to 3:00pm
Title:  Anti-Urysohn spaces
Abstract: please see attached pdf or visit http://www.fields.utoronto.ca/talks/Anti-Urysohn-spaces

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Talk Tomorrow by Itsvan Juhasz at 1 30 pm (Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Itsvan Juhasz
Date and Time: Friday, May 7th, 2021 - 1:30pm to 3:00pm
Title:  Anti-Urysohn spaces
Abstract: please see attached pdf or visit http://www.fields.utoronto.ca/talks/Anti-Urysohn-spaces

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, May 3, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, May 3rd, 4.15-6.15 (NY time)
Title: Marsilius of Inghen, John Buridan and the Semantics of Impossibility

Abstract: In the 14th-century, imaginable yet in some sense impossible non-entities start playing a crucial role in logic, natural philosophy and metaphysics. Throughout the later middle ages and well into early modernity, Marsilius of Inghen’s name comes to be unavoidably associated with the semantics of imaginable impossibilities in most logical and metaphysical discussions. In this paper I analyse Marsilius of Inghen’s semantic treatment of impossible referents, through a comparison with John Buridan’s. While in many ways Marsilius is profoundly influenced by Buridan’s philosophy, his semantic analysis of impossibilia is radically different from Buridan’s. Overall, Buridan tends to analyse away impossible referents in terms of complex concepts by combining possible simple individual parts. Marsilius, on the one hand, treats impossibilia as imaginable referents that are properly unitary; on the other hand, he extends the scope of his modal semantics beyond the inclusion of merely relative impossibilities, allowing for a full semantic treatment of absolute impossibilities as well. Here, I will explore the extent of these differences between Buridan’s and Marsilius of Inghen’s semantics, their presuppositions, and their respective conceptual impact on early modern philosophy of logic and mathematics.

- - - - Tuesday, May 4, 2021 - - - -

- - - - Wednesday, May 5, 2021 - - - -

- - - - Thursday, May 6, 2021 - - - -

Philog Seminar
Thursday May 6, 2021, 6:30 PM
Nietzsche on, Logic, Philosophy, and Moral Values

Introduction: Studies in logic rarely ever mention Fredrich Nietzsche.  There is very little literature on Nietzsche’s critique of classical logic and there is no indication that he followed the developments that were occurring in the field in the 19th century by contemporaneous thinkers such as George Boole, Frege, or Augustus De Morgan.  Yet, logic is central to Nietzsche’s seminal work Beyond Good and Evil: Prelude to a Philosophy of the Future, henceforth referred to as BGE.  Believing that classical logic falsely reinforces the religious promise of absolutism and certainty, Nietzsche rejects the possibility of a priori truths qua truth, but embraces logic to the extent that he considers it the vehicle that systematically discharges a philosopher’s energy and morality onto the world.

In this talk I consider Nietzsche’s critique of moral values as they relate to his rejection of both a priori truths and the semantic principle of bivalence, or what he calls the “faith of opposite values”.  I argue that Nietzsche’s approach to philosophy, logic, and moral values heralds the future philosophical significance of multivalent systems and paraconsistent logic.

A Zoom link will be posted on  https://philog.arthurpaulpedersen.org/

- - - - Friday, May 7, 2021 - - - -

Set Theory Seminar
Friday, May 7, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Benjamin Goodman, CUNY
Woodin's Extender Algebra

This oral exam talk will present a proof of Woodin's result that every real number is generic over some iterated ultrapower of any model with a Woodin cardinal. No fine structure theory will be used, and there will be a brief introduction to iteration trees.

Next Week in Logic at CUNY:

- - - - Monday, May 10, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, May 10th, 4.15-6.15 (NY time)
Filippo Casati (Lehigh)

Title: Heidegger on the Limits and Possibilities of Human Thinking

Abstract: In my talk, I will address what Heidegger calls ‘the basic problem’ of his philosophy, that is, the alleged incompatibility between the notion of Being, our thinking, and logic. First of all, I will discuss some of the ways in which Heideggerians have dealt with this incompatibility by distinguishing what I call the irrationalist and rationalist interpretation. Secondly, I will argue that these two interpretations face both exegetical and philosophical problems. To conclude, I will defend an alternative way to address the incompatibility between the notion of Being, our thinking, and logic. I will argue that, in some of his late works, Heidegger seems to suggest that the real problem lies in the philosophical illusion that we can actually assess the limits of our thinking and, therewith, our logic. Heidegger’s philosophy, I deem, wants to free us from such a philosophical illusion by delivering an experience which reminds us that our thinking is something we can never ‘look at from above’ in order to either grasp its limits or realize that it has no limits whatsoever.

- - - - Tuesday, May 11, 2021 - - - -

- - - - Wednesday, May 12, 2021 - - - -

- - - - Thursday, May 13, 2021 - - - -

- - - - Friday, May 14, 2021 - - - -

Set Theory Seminar
Friday, May 14, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Corey Switzer, University of Vienna

- - - - Other Logic News - - - -

- - - - Web Site - - - -

"Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)"

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## (KGRC) research seminar talk on Thursday, May 6

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, May 6 "Absolute model companionship, the continuum problem, and forcibility" Matteo Viale (Università degli Studi di Torino, Italy) Absolute model companionship (AMC) is a strengthening of model companionship defined as follows: For a theory $T$, $T_{\exists\vee\forall}$ denotes the logical consequences of $T$ which are boolean combinations of universal sentences. $T^*$ is the AMC of $T$ if it is model complete and $T_{\exists\vee\forall}=T^*_{\exists\vee\forall}$. The theory $\mathsf{ACF}$ of algebraically closed field is the model companion of the theory $\mathsf{Fields}$ of fields but not its AMC as $\exists x(x^2+1=0)\in \mathsf{ACF}_{\exists\vee\forall}\steaminess\mathsf{Fields}_{\exists\vee\forall}$. Any model complete theory $T$ is the AMC of $T_{\exists\vee\forall}$. We use AMC to study the continuum problem and to gauge the expressive power of forcing. We show that (a definable version of) $2^{\aleph_0}=\aleph_2$ is the unique solution to the continuum problem which can be in the AMC of a \emph{partial Morleyization} of the $\in$-theory $\ZFC$ enriched with large cardinal axioms. We also show that (assuming large cardinals) forcibility overlaps with the apparently stronger notion of consistency for any mathematical problem $\psi$ expressible as a $\Pi_2$-sentence of a (very large fragment of) third order arithmetic ($\CH$, the Suslin hypothesis, the Whitehead conjecture for free groups, are a small sample of such problems $\psi$). Partial Morleyizations can be described as follows: let $F_{\tau}$ be the set of first order $\tau$-formulae; for $A\subseteq F_\tau$, $\tau_A$ is the expansion of $\tau$ adding atomic relation symbols $R_\phi$ for all formulae $\phi$ in $A$ and $T_{\tau,A}$ is the $\tau_A$-theory asserting that each $\tau$-formula $\phi(\vec{x})\in A$ is logically equivalent to the corresponding atomic formula $R_\phi(\vec{x})$. For a $\tau$-theory $T$, $T+T_{\tau,A}$ is the \emph{partial Morleyization} of $T$ induced by $A\subseteq F_\tau$. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## (KGRC) research seminar talk on Thursday, April 29

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, April 29 "Fullness and mixing property for boolean valued models" Moreno Pierobon (Università di Pisa, Italy) Besides being one of the classical approaches to forcing, boolean valued models provide a flexible tool to produce a variety of structures. In this talk, we will investigate in details the fullness property and the mixing property for boolean valued models. The former is necessary to control the semantics when quotienting a boolean valued model by an ultrafilter. The latter implies the former and it is easier to check. We will show that not every model is full, and the mixing property in not equivalent to fullness. Moreover, we will improve the classical Łoś Theorem for boolean valued models. In the end, we will give a simple characterization of the mixing property using étalé spaces. This last result is an easy corollary of a more general study we made on the categorical equivalence between boolean valued models and presheaves. This is a joint work with Matteo Viale. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Apr 26, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 26th, 4.15-6.15 (NY time)
Rohan French (UC Davis).
Title: Non-Classical Metatheory

Abstract: A common line of thinking has it that proponents of non-classical logics who claim that their preferred logic L gives the correct account of validity, while at the same time giving proofs of theorems about L using classical logic, are in some sense being insincere in their claim that L is the correct logic. This line of thought quite naturally motivates a correctness requirement on a non-classical logic L: that it be able to provide internally acceptable proofs of its main metatheorems. Of central importance amongst such metatheorems will typically be soundness and completeness results, such results being apt to play important roles in arguments showing that a given logic gives the correct account of validity. On the face of it this sounds like a reasonable requirement, but determining its precise content requires us to settle two important conceptual questions: what counts as a completeness proof for a logic, and what does it mean for a result to be internally acceptable? To get clearer on this issue we will look at three different results which have some claim to being internally acceptable soundness and completeness proofs, focusing for ease of comparison on the case of intuitionistic propositional logic, examining the extent to which they can be said to provide internally acceptable soundness and completeness results.

- - - - Tuesday, Apr 27, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 20, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Dave Marker, University of Illinois at Chicago
Real closures of ω1ω1-like models of PA

D'Aquino, Knight and Starchenko showed the real closure of a model of Peano Arithmetic is recursively saturated. Thus any two countable models of PA with the same standard system have isomorphic real closures. Charlie Steinhorn, Jim Schmerl and I showed that even for ω1ω1-like model of PA the situation is very different. We construct 212ℵ1 recursively saturated elementarily equivalent ω1ω1-like models of PA with the same standard system and non-isomorphic real closures.

- - - - Wednesday, Apr 28, 2021 - - - -

- - - - Thursday, Apr 29, 2021 - - - -

- - - - Friday, Apr 30, 2021 - - - -

Set Theory Seminar
Friday, Apr 30, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Elliot Glazer, Harvard University

We define a set of real numbers to be perfectly small if it has perfectly many disjoint translates. Such sets have a strong intuitive claim to being probabilistically negligible, yet no non-trivial measure assigns them all a value of 0. We will prove from a moderate amount of choice that any total extension of Lebesgue measure concentrates on a perfectly small set, suggesting that for any such measure, translation-invariance fails 'as badly as possible.' From the ideas of this proof, we will also derive analogues of well-known paradoxes of randomness, specifically Freiling's symmetry paradox and the infinite prisoner hat puzzle, in terms of perfectly small sets. Finally, we discuss how these results constrain what a paradox-free set theory can look like and some related open questions.

Next Week in Logic at CUNY:

- - - - Monday, May 3, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, May 3rd, 4.15-6.15 (NY time)
Title: Marsilius of Inghen, John Buridan and the Semantics of Impossibility

Abstract: In the 14th-century, imaginable yet in some sense impossible non-entities start playing a crucial role in logic, natural philosophy and metaphysics. Throughout the later middle ages and well into early modernity, Marsilius of Inghen’s name comes to be unavoidably associated with the semantics of imaginable impossibilities in most logical and metaphysical discussions. In this paper I analyse Marsilius of Inghen’s semantic treatment of impossible referents, through a comparison with John Buridan’s. While in many ways Marsilius is profoundly influenced by Buridan’s philosophy, his semantic analysis of impossibilia is radically different from Buridan’s. Overall, Buridan tends to analyse away impossible referents in terms of complex concepts by combining possible simple individual parts. Marsilius, on the one hand, treats impossibilia as imaginable referents that are properly unitary; on the other hand, he extends the scope of his modal semantics beyond the inclusion of merely relative impossibilities, allowing for a full semantic treatment of absolute impossibilities as well. Here, I will explore the extent of these differences between Buridan’s and Marsilius of Inghen’s semantics, their presuppositions, and their respective conceptual impact on early modern philosophy of logic and mathematics.

- - - - Tuesday, May 4, 2021 - - - -

- - - - Wednesday, May 5, 2021 - - - -

- - - - Thursday, May 6, 2021 - - - -

- - - - Friday, May 7, 2021 - - - -

Set Theory Seminar
Friday, May 7, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Benjamin Goodman, CUNY

- - - - Other Logic News - - - -

- - - - Web Site - - - -

"Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)"

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Yair Hayut (Hebrew University, Jerusalem)
TITLE: omega-strongly measurable cardinals
DATE: 28 April 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Two CMU events on Tuesday, April 27

Carnegie Mellon Logic Seminar
TUESDAY, April 27, 2021 Mathematical logic seminar: 3:30 P.M., Online, Omer Ben-Neria, The Hebrew University of Jerusalem Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Tree-like scales and free subsets of set theoretic algebras, part 1 ABSTRACT: In his PhD thesis, Luis Pereira isolated and developed several principles of singular cardinals that emerge from Shelah's PCF theory; principles which involve properties of scales, such as the inexistence of continuous Tree Like scales, and properties of internally approachable structures such as the Approachable Free Subset Property. In the first talk, I will discuss these principles and their relations, and present new results from a joint work with Dominik Adolf concerning their consistency and consistency strength. The second talk will focus on the extender-based Prikry forcing and its connection with these principles. TUESDAY, April 27, 2021 Set Theory Reading Group: 4:30 P.M., Online, Omer Ben-Neria, The Hebrew University of Jerusalem Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Tree-like scales and free subsets of set theoretic algebras, part 2 ABSTRACT: In his PhD thesis, Luis Pereira isolated and developed several principles of singular cardinals that emerge from Shelah's PCF theory; principles which involve properties of scales, such as the inexistence of continuous Tree Like scales, and properties of internally approachable structures such as the Approachable Free Subset Property. In the first talk, I will discuss these principles and their relations, and present new results from a joint work with Dominik Adolf concerning their consistency and consistency strength. The second talk will focus on the extender-based Prikry forcing and its connection with these principles.

## (KGRC) research seminar talk on Thursday, April 22

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, April 22 "MAD families and strategically bounding forcings" Osvaldo Guzmán (Universidad Nacional Autónoma de México) The notion of strategically bounding forcings is a natural game-theoretic strengthening of the bounding property for partial orders. In this talk, we will study the basic properties of strategically bounding forcings and talk about indestructibility of MAD families. The motivation for this work is the problem of Roitman. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Apr 19, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 19th, 4.15-6.15 (NY time)
V. Alexis Peluce (CUNY)
Title: Brouwer’s First Act of Intuitionism

Abstract: L.E.J. Brouwer famously argued that mathematics was completely separated from formal language. His explanation for why this is so leaves room for interpretation. Indeed, one might ask: what sort of philosophical background is required to make sense of the strong anti-linguistic views of Brouwer? In this talk, we outline some possible answers to the above. We then present an interpretation that we argue best makes sense of Brouwer’s first act.

- - - - Tuesday, Apr 20, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 20, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Cordón Franco Universidad de Sevilla

Induction and collection up to definable elements: calibrating the strength of parameter-free ΔnΔn-minimization.

In this talk we shall deal with fragments of first-order Peano Arithmetic obtained by restricting the conclusion of the induction or the collection axiom to elements in a prescribed subclass DD of the universe. Fix n>0n>0. The schemes of ΣnΣn-induction up to ΣmΣm-definable elements and the schemes of ΣnΣn-collection up to ΣmΣm-definable elements form two families of subtheories of IΣnIΣn and BΣnBΣn, respectively, obtained in this way.

The properties of ΣnΣn-induction up to ΣmΣm-definable elements for nmn≥m are reasonably well understood and interesting applications of these fragments are known. However, an analysis of the case n<mn<m was pending. In the first part of this talk, we address this problem and show that it is related to the following general question: 'Under which conditions on a model MM can we prove that every non-empty ΣmΣm-definable subset of MM contains some ΣmΣm-definable element?'

In the second part of the talk, we show that, for each n1n≥1, the scheme of ΣnΣn-collection up to ΣnΣn-definable elements provides us with an axiomatization of the Σn+1Σn+1-consequences of BΣnBΣn. As an application, we obtain that BΣnBΣn is Σn+1Σn+1-conservative over parameter-free ΔnΔn-minimization (plus IΣn1n−1), thus partially answering a question of R. Kaye.

This is joint work with F.Félix Lara-Martín (University of Seville).

- - - - Wednesday, Apr 21, 2021 - - - -

- - - - Thursday, Apr 22, 2021 - - - -

Philog Seminar
Thursday, April 22, 2021, 6:30 PM
Todd Stambaugh (John Jay)
Knowledge, behavior, and rationality: Rationalizability in epistemic games

Abstract:  In strategic situations, agents base actions on knowledge and beliefs.  This  includes  knowledge  about  others’  strategies  and  preferences  over strategy profiles, but also about other external factors. Bernheim  and  Pearce  in  1984  independently  defined  the  game  theoretic solution concept of rationalizability, which is built on the premise that rational agents will only take actions that are the best response to some situation that they  consider  possible.

This  accounts  for  other  agents’  rationality  as  well, limiting  the  strategies  to  which  a  particular  agent  must  respond,  enabling further elimination until the strategies stabilize. We seek to generalize rationalizability to account not only for actions, but knowledge of the world as well. This will enable us to examine the interplay between  action  based  and  knowledge  based  rationality.

We  give  an  account of what it means for an action to be rational relative to a particular state of affairs, and in turn relative to a state of knowledge. We  present  a  class  of  games,  Epistemic  Messaging  Games  (EMG),  with a  communication  stage  that  clarifies  the  epistemic  state  among  the  players prior  to  the  players’  actions.  We  use  a  history  based  model,  which  frames individual  knowledge  in  terms  of  local  projections  of  a  global  history.  With this framework, we give an account of rationalizability for subclasses of EMG

(Joint work with Rohit Parikh.  Todd Stambaugh received his doctorate in 2018, from the mathematics program of CUNY).

A Zoom link will be posted on philog.arthurpaulpedersen.org on Wednesday

- - - - Friday, Apr 23, 2021 - - - -

Set Theory Seminar
Friday, Apr 23, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Andrés Villaveces, Universidad Nacional de Colombia – Bogotá
Two logics, and their connections with large cardinals / Questions for BDGM: Part II

In the past couple of years I have been involved (joint work with Väänänen and independently with Shelah) with some logics in the vicinity of Shelah's L1κLκ1 (a logic from 2012 that has Interpolation and a very weak notion of compactness, namely Strong Undefinability of Well-Orderings, and in some cases has a Lindström-type theorem for those two properties). Our work with Väänänen weakens the logic but keeps several properties. Our work with Shelah explores the connection with definability of AECs.

These logics seem to have additional interesting properties under the further assumption of strong compactness of a cardinal, and this brings them close to recent work of Boney, Dimopoulos, Gitman and Magidor [BDGM].

During the first lecture, I plan to describe two games and a syntax of two logics: Shelah's L1κLκ1 and my own logic (joint work with Väänänen) L1,cκLκ1,c. I will stress some of the properties of these logics, without any use of large cardinal assumptions.

During the second lecture, I plan to enter rather uncharted territory. I will describe some constructions done by Shelah (mostly) under the assumption of strong compactness, but I also plan to bring these logics to a territory closer to the work of [BDGM]. This second lecture will have more conjectures, ideas, and (hopefully interesting) discussions with some of the authors of that paper.

Next Week in Logic at CUNY:

- - - - Monday, Apr 26, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 26th, 4.15-6.15 (NY time)
Rohan French (UC Davis).
Title: Non-Classical Metatheory

Abstract: A common line of thinking has it that proponents of non-classical logics who claim that their preferred logic L gives the correct account of validity, while at the same time giving proofs of theorems about L using classical logic, are in some sense being insincere in their claim that L is the correct logic. This line of thought quite naturally motivates a correctness requirement on a non-classical logic L: that it be able to provide internally acceptable proofs of its main metatheorems. Of central importance amongst such metatheorems will typically be soundness and completeness results, such results being apt to play important roles in arguments showing that a given logic gives the correct account of validity. On the face of it this sounds like a reasonable requirement, but determining its precise content requires us to settle two important conceptual questions: what counts as a completeness proof for a logic, and what does it mean for a result to be internally acceptable? To get clearer on this issue we will look at three different results which have some claim to being internally acceptable soundness and completeness proofs, focusing for ease of comparison on the case of intuitionistic propositional logic, examining the extent to which they can be said to provide internally acceptable soundness and completeness results.

- - - - Tuesday, Apr 27, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 20, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Dave Marker, University of Illinois at Chicago
Real closures of ω1ω1-like models of PA

D'Aquino, Knight and Starchenko showed the real closure of a model of Peano Arithmetic is recursively saturated. Thus any two countable models of PA with the same standard system have isomorphic real closures. Charlie Steinhorn, Jim Schmerl and I showed that even for ω1ω1-like model of PA the situation is very different. We construct 212ℵ1 recursively saturated elementarily equivalent ω1ω1-like models of PA with the same standard system and non-isomorphic real closures.

- - - - Wednesday, Apr 28, 2021 - - - -

- - - - Thursday, Apr 29, 2021 - - - -

- - - - Friday, Apr 30, 2021 - - - -

Set Theory Seminar
Friday, Apr 30, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Elliot Glazer, Harvard University

- - - - Other Logic News - - - -

- - - - Web Site - - - -

"Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)"

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Barcelona Set theory Seminar

Barcelona Logic Seminar
Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Sam Roberts (Universität Konstanz)
TITLE: Reinhardt’s potentialism
DATE: 21 April 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## Tomorrow talk by Micheal Hrusak (1:30 pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Micheal Hrusak
Date and Time: Friday, April 16th, 2021 - 1:30pm to 3:00pm
Title:  Ultrafiters, MAD families and the Kat\v{e}tov order
Abstract: We shall survey recent results concerning classification of MAD
families and ultrafilters using the Kat\v{e}tov order, concentrating on
open problems.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Friday 16th talk by Micheal Hrusak (1:30 pm Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please use the following link and fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Micheal Hrusak
Date and Time: Friday, April 16th, 2021 - 1:30pm to 3:00pm
Title:  Ultrafiters, MAD families and the Kat\v{e}tov order
Abstract: We shall survey recent results concerning classification of MAD
families and ultrafilters using the Kat\v{e}tov order, concentrating on
open problems.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## (KGRC) research seminar talk on Thursday, April 15

Kurt Godel Research Center
Research seminar Kurt Gödel Research Center Thursday, April 15 "Choice, Groups, and Topoi" Andreas Blass (University of Michigan) Work of Tarski, Mostowski, Gauntt, and Truss provides finite, group-theoretic criteria for ZF-provability of implications between weak choice axioms of the form "every family of n-element sets has a choice function" or "every countable family of n-element sets has a choice function." From a sufficiently broad, category-theoretic viewpoint, these implications and the equivalent group-theoretic criteria look like exactly the same statements but interpreted in different categories, namely certain particular sorts of topoi. The main result is that this equivalence applies not only to these particular sorts of topoi but to all topoi. I plan to describe the ingredients of this work --- choice principles, group properties, and topoi --- and, if time permits, give a hint about the ideas in the proofs. Time and Place Talk at 3:00pm via Zoom: This talk will be given via Zoom. If you have not received the meeting link by the day before the talk, please contact richard.springer@univie.ac.at!

## Two talks on Tuesday, April 20

Carnegie Mellon Logic Seminar
TUESDAY, April 20, 2021 Mathematical logic seminar: 3:30 P.M., Online, Sandra Müller, University of Vienna Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: Large cardinals and determinacy when all sets are universally Baire ABSTRACT: The large cardinal strength of the Axiom of Determinacy when enhanced with the hypothesis that all sets of reals are universally Baire is known to be much stronger than the Axiom of Determinacy itself. In fact, Sargsyan conjectured it to be as strong as the existence of a cardinal that is both a limit of Woodin cardinals and a limit of strong cardinals. Larson, Sargsyan and Wilson showed that this would be optimal via a generalization of Woodin's derived model construction. After a gentle introduction to the connection between determinacy axioms and large cardinals we will sketch a proof of Sargsyan's conjecture. TUESDAY, April 20, 2021 Set Theory Reading Group: 4:30 P.M., Online, Sandra Müller, University of Vienna Join Zoom Meeting: https://cmu.zoom.us/j/621951121 [cmu.zoom.us] Meeting ID: 621 951 121 TITLE: The exact consistency strength of "AD + all sets are universally Baire" ABSTRACT: In this second talk, we will outline the proof of Sargsyan's conjecture with more details. In particular, we will discuss a new translation procedure for hybrid mice extending work of Steel, Zhu and Sargsyan that is crucial in the construction of a model with a cardinal that is both a limit of Woodin cardinals and a limit of strong cardinals from a model of the Axiom of Determinacy in which all sets of reals are universally Baire.

## UPDATE: This Week in Logic at CUNY

This Week in Logic at CUNY
Hi everyone,

Additional details have been added for this Thursday's talk by Joe Halpern in the Philog Seminar.

Best,
Jonas

This Week in Logic at CUNY:

- - - - Monday, Apr 12, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 12th, 4.15-6.15 (NY time)
William Nava (NYU)
Title: Logical deducibility and substitution in Bolzano (and beyond)

Abstract: Bolzano is famously responsible for an influential substitutional account of logical consequence (or, as he calls it, logical deducibility): a proposition, 𝜑, is logically deducible from a set of propositions, Γ, iff every uniform substitution of non-logical ideas in Γ∪{𝜑} that makes every proposition in Γ true also makes 𝜑 true. There are two problems with making sense of Bolzano’s proposal, however. One is that Bolzano argues that every proposition is of the form a has B—in other words, is a monadic atomic predication. So, for Bolzano, logically complex propositions like ‘𝜑 and 𝜓’ cannot have the semantic structure they appear to. This can be addressed, roughly, by taking complex propositions to predicate logical ideas of collections of propositions. But this introduces the second problem: for Bolzano, familiar logical ideas like ‘and’, ‘or’, and ‘not’ are complex ideas with compositional structure. I’ll show that, as a result of this structure, we cannot use the simple and familiar notion of uniform substitution in order to understand logical deducibility. We must instead use what I’ll call form-sensitive substitution. I will end by drawing some general lessons about substitutional definitions of logical consequence in languages with the resources to generate complex predicates of propositions.

- - - - Tuesday, Apr 13, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 13, 7pm
The seminar will take place virtually at 7pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Roman Kossak, CUNY
Automorphisms, Jónsson Models, and Satisfaction Classes

25 years ago I wrote a paper on four open problems concerning recursively saturated models of PA. The problems are still open. I will talk about two of them: (1) Let M be a countable recursively saturated model of PA. Can every automorphism of M be extended to some recursively saturated elementary end extension of M? (2) Is there a recursively saturated model of PA that has no recursively saturated elementary submodel of the same cardinality as the model? I will present some partial results involving partial inductive satisfaction classes.

- - - - Wednesday, Apr 14, 2021 - - - -

- - - - Thursday, Apr 15, 2021 - - - -

Philog Seminar
Thursday, April 15, 6:30 PM
Joe Halpern, Cornell University
Actual Causality: A Survey

What does it mean that an event C actually caused'' event E?
The problem of defining actual causation goes beyond mere philosophical
speculation.  For example, in many legal arguments, it is precisely what
needs to be established in order to determine responsibility. (What exactly
was the actual cause of the car accident or the medical problem?)
The philosophy literature has been struggling with the problem
of defining causality since the days of Hume, in the 1700s.
Many of the definitions have been couched in terms of counterfactuals.
(C is a cause of E if, had C not happened, then E would not have happened.)
In 2001, Judea Pearl and I introduced a new definition of actual cause,
using Pearl's notion of structural equations to model
counterfactuals.  The definition has been revised twice since then,
extended to deal with notions like "responsibility" and "blame", and
applied in databases and program verification.  I survey
the last 15 years of work here, including joint work
with Judea Pearl, Hana Chockler, and Chris Hitchcock.  The talk will be
completely self-contained.

A Zoom link will be posted on April 14 on https://philog.arthurpaulpedersen.org/

- - - - Friday, Apr 16, 2021 - - - -

Set Theory Seminar
Friday, Apr 16, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Villaveces CUNY

Next Week in Logic at CUNY:

- - - - Monday, Apr 19, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 19th, 4.15-6.15 (NY time)
V. Alexis Peluce (CUNY)
Title: Brouwer’s First Act of Intuitionism

Abstract: L.E.J. Brouwer famously argued that mathematics was completely separated from formal language. His explanation for why this is so leaves room for interpretation. Indeed, one might ask: what sort of philosophical background is required to make sense of the strong anti-linguistic views of Brouwer? In this talk, we outline some possible answers to the above. We then present an interpretation that we argue best makes sense of Brouwer’s first act.

- - - - Tuesday, Apr 20, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 20, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Cordón Franco Universidad de Sevilla

- - - - Wednesday, Apr 21, 2021 - - - -

- - - - Thursday, Apr 22, 2021 - - - -

- - - - Friday, Apr 23, 2021 - - - -

Set Theory Seminar
Friday, Apr 23, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Villaveces CUNY

- - - - Other Logic News - - - -

- - - - Web Site - - - -

"Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)"

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Logic Seminar 14 April 2021 17:00 hrs by Karen Seidel, HPI, University of Potsdam

NUS Logic Seminar
Invitation to the Logic Seminar at the National University of Singapore Date: Wednesday, 14 April 2020, 17:00 hrs Talk via Zoom: https://nus-sg.zoom.us/j/96860201432?pwd=cVdwZmd2clVFaEhaTmJjaGdXMFdmdz09 Meeting ID: 968 6020 1432 Password: Is P=NP? Speaker: Karen Seidel Title: Learning from informant URL: http://www.comp.nus.edu.sg/~fstephan/logicseminar.html Abstract: Learning from positive and negative information, so called informant, is one of the models for human and machine learning introduced by Gold. We review existing classical and recent results regarding the learning power of associated settings.

## Barcelona Set theory Seminar

Barcelona Logic Seminar

Dear All,

Please find attached the announcement of the next session of the Barcelona Set Theory Seminar. Feel free to distribute it.

SPEAKER:   Erin Carmody (Fordham University)
TITLE: The relationships between measurable and strongly compact cardinals
DATE: 14 April 2021
TIME: 16:00 (CEST)
PLACE: The Seminar will take place online at the following address:

Best regards,
Joan

P.S.: If you do not wish to receive any more announcements, please send an email to bagaria@ub.edu with the text “Unsubscribe”.

Joan Bagaria
ICREA Research Professor
Universitat de Barcelona
Departament de Matemàtiques i Informàtica
Gran Via de les Corts Catalanes 585
08007 Barcelona
Catalonia

Phone: +34 93 402 1609

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Apr 12, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 12th, 4.15-6.15 (NY time)
William Nava (NYU)
Title: Logical deducibility and substitution in Bolzano (and beyond)

Abstract: Bolzano is famously responsible for an influential substitutional account of logical consequence (or, as he calls it, logical deducibility): a proposition, 𝜑, is logically deducible from a set of propositions, Γ, iff every uniform substitution of non-logical ideas in Γ∪{𝜑} that makes every proposition in Γ true also makes 𝜑 true. There are two problems with making sense of Bolzano’s proposal, however. One is that Bolzano argues that every proposition is of the form a has B—in other words, is a monadic atomic predication. So, for Bolzano, logically complex propositions like ‘𝜑 and 𝜓’ cannot have the semantic structure they appear to. This can be addressed, roughly, by taking complex propositions to predicate logical ideas of collections of propositions. But this introduces the second problem: for Bolzano, familiar logical ideas like ‘and’, ‘or’, and ‘not’ are complex ideas with compositional structure. I’ll show that, as a result of this structure, we cannot use the simple and familiar notion of uniform substitution in order to understand logical deducibility. We must instead use what I’ll call form-sensitive substitution. I will end by drawing some general lessons about substitutional definitions of logical consequence in languages with the resources to generate complex predicates of propositions.

- - - - Tuesday, Apr 13, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 13, 7pm
The seminar will take place virtually at 7pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Roman Kossak, CUNY
Automorphisms, Jónsson Models, and Satisfaction Classes

25 years ago I wrote a paper on four open problems concerning recursively saturated models of PA. The problems are still open. I will talk about two of them: (1) Let M be a countable recursively saturated model of PA. Can every automorphism of M be extended to some recursively saturated elementary end extension of M? (2) Is there a recursively saturated model of PA that has no recursively saturated elementary submodel of the same cardinality as the model? I will present some partial results involving partial inductive satisfaction classes.

- - - - Wednesday, Apr 14, 2021 - - - -

- - - - Thursday, Apr 15, 2021 - - - -

Philog Seminar
Thursday, April 8, 6:30 PM
Speaker: Joseph Halpern, Cornell

- - - - Friday, Apr 16, 2021 - - - -

Set Theory Seminar
Friday, Apr 16, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Villaveces CUNY

Next Week in Logic at CUNY:

- - - - Monday, Apr 19, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 19th, 4.15-6.15 (NY time)
V. Alexis Peluce (CUNY)
Title: Brouwer’s First Act of Intuitionism

Abstract: L.E.J. Brouwer famously argued that mathematics was completely separated from formal language. His explanation for why this is so leaves room for interpretation. Indeed, one might ask: what sort of philosophical background is required to make sense of the strong anti-linguistic views of Brouwer? In this talk, we outline some possible answers to the above. We then present an interpretation that we argue best makes sense of Brouwer’s first act.

- - - - Tuesday, Apr 20, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 20, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Cordón Franco Universidad de Sevilla

- - - - Wednesday, Apr 21, 2021 - - - -

- - - - Thursday, Apr 22, 2021 - - - -

- - - - Friday, Apr 23, 2021 - - - -

Set Theory Seminar
Friday, Apr 23, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Andrés Villaveces CUNY

- - - - Other Logic News - - - -

- - - - Web Site - - - -

"Find us on the web at:  nylogic.github.io
(site designed, built & maintained by Victoria Gitman)"

If you have a logic-related event that you would like included in future mailings, please email jreitz@nylogic.org

## Unusual time for tomorrow talk by Joerg Brendle (10:30 am Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please remember that Toronto just had a daylight saving change of time and please notice the UNUSUAL TIME.

Please use the following link and fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Joerg Brendle
Date and Time: Friday, April 9th, 2021 - 10:30am to 12:00pm
Title: Combinatorics of ultrafilters on complete Boolean algebras
Abstract:
The combinatorial structure of ultrafilters on the natural numbers has been investigated intensively for many decades, and a lot is known about the order structure of such ultrafilters (under either the Tukey or the Rudin-Keisler ordering), about special classes of ultrafilters (like P-points),or about cardinal invariants related to ultrafilters (like the ultrafilter number). Yet, very little has beendone so far concerning combinatorial aspects of ultrafilters on general Boolean algebras, and thepurpose of this talk will be to present some basic results in this direction.

Focus will be put on the Tukey ordering, on (non)existence of non-Tukey-maximal ultrafilters, on ultrafilter numbers, and on an analogue of the Rudin-Keisler ordering in the context of complete Boolean algebras. We will in particular deal with Cohen and random algebras. This is joint work with Francesco Parente.

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## Unusual time for Friday 9th talk by Joerg Brendle (10:30 am Toronto time)

Toronto Set Theory Seminar
Hello everyone,

Please remember that Toronto just had a daylight saving change of time and please notice the UNUSUAL TIME.

Please use the following link and fill the form (every week) to enter the meeting. This form helps the Field Institute to know statistical data about attendance.

Here the speaker information:

Speaker: Joerg Brendle
Date and Time: Friday, April 9th, 2021 - 10:30am to 12:00pm
Title: Combinatorics of ultrafilters on complete Boolean algebras
Abstract:
The combinatorial structure of ultrafilters on the natural numbers has been investigated intensively for many decades, and a lot is known about the order structure of such ultrafilters (under either the Tukey or the Rudin-Keisler ordering), about special classes of ultrafilters (like P-points),or about cardinal invariants related to ultrafilters (like the ultrafilter number). Yet, very little has beendone so far concerning combinatorial aspects of ultrafilters on general Boolean algebras, and thepurpose of this talk will be to present some basic results in this direction.

Focus will be put on the Tukey ordering, on (non)existence of non-Tukey-maximal ultrafilters, on ultrafilter numbers, and on an analogue of the Rudin-Keisler ordering in the context of complete Boolean algebras. We will in particular deal with Cohen and random algebras. This is joint work with Francesco Parente.

Best

Iván Ongay Valverde (he/his)

My email account ongay@math.wisc.edu will be closed in October 2020. Please contact me either at ongay@yorku.ca or at ivan.ongay.valverde@gmail.com

## This Week in Logic at CUNY

This Week in Logic at CUNY
This Week in Logic at CUNY:

- - - - Monday, Apr 5, 2021 - - - -

Logic and Metaphysics Workshop
Spring 2021
Date: Monday, April 5th, 4.15-6.15 (NY time)
Speakers: Federico Pailos and Eduardo Barrio (Buenos Aires)
Title: A Metainferential Solution to the Adoption Problem

Abstract: In ‘The Question of Logic’ (Kripke 2020) and “The Adoption Problem and the Epistemology of Logic” (Padró 2020), Kripke and Padró argue against the possibility of adopting an alternative logic. Without having already endorsed a logic, it is not possible to derive the consequences of an alternative system. In particular, without Modus Ponens in the metatheory, one could not adopt any inferential rule at all. This seems to cause trouble for logics like LP, that does not validate this rule. Modus Ponens is a self-governing rule that cannot be adopted and could not be rejected. This is connected with the problem of the tortoise reasoner (Scambler 2019) and the problem of the tortoise Logic (Priest 2021). In this talk, we offer a new solution. With the metainferential logic TS/LP it is possible to model metalogical Modus Ponens-like reasoning while still rejecting Modus Ponens.

- - - - Tuesday, Apr 6, 2021 - - - -

Models of Peano Arithmetic (MOPA)
Tuesday, April 6, 7pm
The seminar will take place virtually at 7pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.
Zachiri McKenzie

Topless powerset preserving end-extensions and rank-extensions of countable models of set theory

This talk will report on ongoing work that is being done in collaboration with Ali Enayat (University of Gothenburg).

For models of set theory NN and MMNN is a powerset preserving end-extension of MM if NN is an end-extension of MM and NN contains no new subsets of sets in MM. A model of Kripke-Platek Set Theory, NN, is a rank-extension of a model of Kripke-Platek Set Theory, MM, if NN is an end-extension of MM and all of the new sets in NN have rank that exceeds the rank of all of the sets in MM. A powerset preserving end-extension (rank-extension) NN of MM is topless if MNMN and there is no set in NMNM containing only sets from MM. If M=M,EMM=⟨M,EM is a model of set theory, then the admissible cover of MMCovMCovM, is defined to be the smallest admissible structure with MM forming its urelements and whose language contains a unary function function symbol, FF, that sends each mMm∈M to the set {xMxEMm}{x∈M∣xEMm}. Barwise has shown that if MM is a model of Kripke-Platek Set Theory, then CovMCovM exists and its minimality facilitates compactness arguments for infinitary languages coded in CovMCovM. We extend Barwise's analysis by showing that if MM satisfies enough set theory then the expansion of CovMCovM obtained by adding the powerset function remains admissible. This allows us to build powerset preserving end-extensions and rank-extensions of countable models of certain subsystems of ZFCZFC satisfying any given recursive subtheory of the model being extended. In particular, we show that

1. Every countable model of KPPKPP has a topless rank-extension that satisfies KPPKPP.
2. Every countable ωω-standard model of MOST+Π1-collectionMOST+Π1-collection has a topless powerset preserving end-extension that satisfies MOST+Π1-collectionMOST+Π1-collection.

- - - - Wednesday, Apr 7, 2021 - - - -

- - - - Thursday, Apr 8, 2021 - - - -

Philog Seminar
Thursday, April 8, 6:30 PM
Speaker: Jongjin (JJ) Kim (Korea University)

Abstract.  We discuss two approaches to life: presentism and futurism. We locate presentism within various elements of Buddhism, in the form of advice to live in the present and not to allow the future to hinder us from living in the ever present now. By contrast, futurism, which we identify with Karl Popper, advises us to think of future consequences before we act, and to act now for a better future. Of course, with its emphasis on a well-defined path to an ideal future ideally culminating in enlightenment, Buddhism undoubtedly has elements of futurism as well. We do not intend to determine which of these two approaches to time is more dominant in Buddhism, nor how the two approaches are best understood within Buddhism; but simply we intend to compare and contrast these two approaches, using those presentist elements of Buddhism as representative of presentism while contrasting them with those elements of futurism to be found in Popper and others. We will discuss various aspects of presentism and futurism, such as Ruth Millikan’s Popperian animal, the psychologist Howard Rachlin’s social and temporal discounting, and even the popular but controversial idea, YOLO (you only live once). The primary purpose of this paper is to contrast one with the other. The central question of ethics is: How should one live? Our variation on that question is: When should one live? We conjecture that the notion of flow, developed by Csikszentmihalyi, may be a better optimal choice between these two positions.

Jongjin Kim received his doctorate in Philosophy from CUNY in 2019.

on Wednesday

- - - - Friday, Apr 9, 2021 - - - -

Set Theory Seminar
Friday, Apr 9, 2pm
The seminar will take place virtually at 2pm US Eastern Standard Time. Please email Victoria Gitman (vgitman@nylogic.org) for meeting id.

Sandra Müller, University of Vienna
The exact consistency strength of 'AD + all sets are universally Baire'

The large cardinal strength of the Axiom of Determinacy when enhanced with the hypothesis that all sets of reals are universally Baire is known to be much stronger than the Axiom of Determinacy itself. In fact, Sargsyan conjectured it to be as strong as the existence of a cardinal that is both a limit of Woodin cardinals and a limit of strong cardinals. Larson, Sargsyan and Wilson showed that this would be optimal via a generalization of Woodin’s derived model construction. We will discuss a new translation procedure for hybrid mice extending work of Steel, Zhu and Sargsyan and use this to prove Sargsyan’s conjecture.

Next Week in Logic at CUNY:

- - - - Monday, Apr 12, 2021 - - - -

Logic and Metaphysics Workshop
Date: Monday, April 5th, 4.15-6.15 (NY time)