Refreshments will be served in the 9th floor lounge at 3:30PM before talks, subject the evolving pandemic conditions.

We will live stream the local logic seminar with the following login information:

Zoom link to local UW logic seminar

Meeting ID: 986 3594 0882

Passcode: 003073

The joint Midwest Computability/Model Theory Seminar will be live streamed
with the following login information:

Zoom link

Meeting ID: 997 5433 2165

Passcode: midwest

- 9/10/2024 4PM,
Steffen Lempp,
UW

Title: Some results on the Ziegler degrees (video and related paper (coming soon))Abstract: In a landmark 1980 monograph, Ziegler studied finitely generated subgroups of existentially closed groups and uncovered a surprising connection of this purely algebraic question and computability. To this end, he defined a new reducibility which he called *-reducibility and which I will call Ziegler reducibility, which is a refinement of both Turing and enumeration reducibility. In particular, he showed that if a finitely generated group H is a subgroup of an existentially closed group G and the word problem of a finitely generated group H_{0}is Ziegler reducible to the word problem of H, then H_{0}is (isomorphic to) a subgroup of G as well.In joint work with Isabella Scott and Josiah Jacobsen-Grocott, I studied the induced degree structure of the Ziegler degrees and was able to show that there is a minimal Ziegler degree, and indeed that any finite distributive lattice is isomorphic to an initial segment of the Ziegler degrees. As a consequence, the ∀∃∀-theory of the Ziegler degrees (as a partial order) is undecidable.

- 9/17/2024 4PM,
Yayi Fu,
UW

Title: O-minimal coherence (video and slides)Abstract: Bakker, Brunebarbe, Tsimerman showed in 2022 that the definable structure sheaf O_{Cn}of**C**^{n}is a coherent O_{Cn}-module as a sheaf on the site, where the coverings are finite coverings by definable open sets.**C**^{n}In general, let K be an algebraically closed field of characteristic zero. We give another proof of the coherence of O

_{Kn}as a sheaf of O_{Kn}-modules on the site__K__using spectral topology on the type space S^{n}_{n}(K). (Here S_{n}(K) just means S_{2n}(R) for some real closed field R.)It also gives an example of how the intuition that sheaves on the type space are the same as sheaves on the site with finite coverings (see Proposition 3.2 in Edmundo (2006)) can be applied.

- 9/24/2024 4PM,
Jake
Fiedler, UW

Title: Bounds on the dimension of lineal extensions (video and slides)Abstract: How does the size of a collection of line segments in**R**^{n}change if we extend each segment to a full line? In this talk, we investigate this problem in geometric measure theory using techniques from algorithmic information theory, specifically Kolmogorov complexity and the point-to-set principle of Lutz and Lutz. Working in the plane, we show that the packing dimension of any set does not increase under line segment extension. This allows us to prove the generalized Kakeya conjecture for packing dimension in the plane. Finally, we discuss versions of this problem in higher dimensions. This is based on joint work with Ryan Bushling. - 10/4/24
(
**department colloquium**), 4PM in**room B239 Van Vleck**,

Su Gao, Nankai University, Tianjin, China

Title: Continuous combinatorics of countable abelian group actions (slides)Abstract: We consider combinatorial problems on the free parts of the Bernoulli shift actions of countable abelian groups, such as chromatic numbers, edge chromatic numbers, perfect matchings, etc. These problems can all be regarded as special cases of the problem whether there exist continuous equivariant maps from the free part of the Bernoulli shift action to a subshift of finite type. We prove a master theorem which in theory gives complete answers to the subshift problem. Furthermore, we show that the class of (codes for) all subshifts of finite type with a positive answer to the subshift problem is a complete c.e. set. This is joint work with Steve Jackson, Ed Krohne, and Brandon Seward.

Dinner: Vintage Brewing Company (676 S. Whitney Way) on**Saturday**, Oct. 5th, at 7PM - 10/7/2024 4PM (
**room TBA**), Liang Yu, Nanjing University, China

Title: When is A + xA =**R**?Abstract: We investigate which algebra substructures A of reals are such that there is a real x for which A+xA=**R**. - 10/8/2024 4PM,
Hongyu Zhu,
UW

Title: Survey on Vaught's Conjecture (specialty exam)Abstract: In 1961, Vaught proposed his conjecture on the number of countable models of a first-order theory. Despite some early progress and attempts from various areas of logic, the conjecture remains unsolved today. In this talk, we will survey certain results around the conjecture, including alternative formulations and solved special cases. In particular, we will discuss Shelah's proof of Vaught's conjecture for complete ω-stable first-order theories and how that relates to my own work in progress. - 10/15/2024 4PM,
Antonio Nakid
Cordero, UW

Title: TBAAbstract: TBA - 10/22/2024 4PM,
Joel Hamkins, University of
Notre Dame, Indiana

Title: TBAAbstract: TBA

Dinner: TBA around 6PM - 10/29/2024 4PM,
Karthik Ravishankar, UW

Title: TBAAbstract: TBA - 11/5/2024 4PM,
Tim
McNicholl, Iowa State University, Ames

Title: The computability of K-theory for operator algebras (joint work with C. Eagle, I. Goldbring, and R. Miller)Abstract: K-theory is a general method for associating countable Abelian groups with mathematical structures. These groups are invariants, but they are not always classifiers. Lately, Chris Eagle, Isaac Goldbring, Russell Miller, and I have been thinking about the computability of K-theory as it applies to operator algebras (i.e., C^{*}-algebras). I will try to explain the machinery of K-theory for operator algebras and explain at least the architecture of the following theorems. 1) If A is a computably presentable C^{*}-algebra, then the Abelian group K_{0}(A) has a c.e. (a.k.a. recursive) presentation. 2) If A is a computably presentable uniformly hyperfinite algebra, then K_{0}(A) has a computable presentation; moreover, the trace of A is computable and its supernatural number is lower semi-computable.

Dinner: TBA around 6PM - 11/12/2023
**Midwest Computability Seminar, University of Chicago, John Crerar Library Building 390**

(live streamed on Zoom, Meeting ID: 997 5433 2165, Passcode: midwest)

Brown bag lunch: in John Crerar Library Building 390 at noon

Speakers:- 1PM, Jake Fiedler, UW

Title: TBAAbstract: TBA

- 1:45PM,
Gabriela Laboska, University of Chicago, Illinois

Title: TBAAbstract: TBA

- 3:15PM, Ang
Li, UW

Title: TBAAbstract: TBA - 4PM, Mariya
Soskova, UW

Title: TBAAbstract: TBA

- 1PM, Jake Fiedler, UW
- 11/19/2024 4PM,
Peter Cholak,
University of Notre Dame, Indiana

Title: TBAAbstract: TBA

Dinner: TBA around 6PM - 11/26/2024 4PM,
TBA

Title: TBAAbstract: TBA - 12/3/2024 4PM,
TBA

Title: TBAAbstract: TBA - 12/10/2024 4PM,
TBA

Title: TBAAbstract: TBA