Virtual Logic Seminars Worldwide
There are two fairly complete virtual logic seminar lists maintained by
and by Anton Bernshteyn.
Two particularly popular, completely virtual logic seminars:
UW Logic Seminar Schedule
All talks for fall 2020 will be virtual. Links are provided below.
The regular "virtual" meeting time is Tuesdays at 3PM during the semester.
We have a joint seminar with other Midwestern logic groups (the
Midwest Computability Seminar) every other week
starting August 18, and local seminars on the other Tuesdays,
with occasional joint meetings with the
The recurring Zoom link for the Midwest Computability Seminar is:
Meeting ID: 997 5433 2165,
The recurring Webex link for the Midwest Model Theory Seminar is:
Meeting number: 126 772 4675,
Password: (the password is stable, but ask me if you don't have it)
The recurring Zoom link for the local UW logic seminar is:
Meeting ID: 970 9130 0913,
- 8/18/2020 3PM (Midwest Computability Seminar),
Title: Redundancy of information: lowering effective
Abstract: A natural way to measure the similarity between two infinite binary
sequences X and Y is to take the (upper) density of their symmetric difference.
This is the Besicovitch distance on Cantor space. If d(X,Y) = 0, then we say
that X and Y are coarsely equivalent. Greenberg, Miller, Shen, and Westrick
(2018) proved that a binary sequence has effective (Hausdorff) dimension 1
if and only if it is coarsely equivalent to a Martin-Löf random sequence.
They went on to determine the best and worst cases for the distance from a
dimension t sequence to the nearest dimension s>t sequence. Thus, the
difficulty of increasing dimension is understood.
Greenberg et al. also determined the distance from a dimension 1 sequence to
the nearest dimension t sequence. But they left open the general problem of
reducing dimension, which is made difficult by the fact that the information
in a dimension s sequence can be coded (at least somewhat) redundantly.
Goh, Miller, Soskova, and Westrick recently gave a complete solution.
I will talk about both the results in the 2018 paper and the more recent work.
In particular, I will discuss some of the coding theory behind these results.
No previous knowledge of coding theory is assumed.
- 8/25/2020 3PM (Midwest Model Theory Seminar),
University of California-Los Angeles
Title: Model-theoretic tree properties
Abstract: The first model-theoretic tree properties were introduced by Shelah
as a by-product of his analysis of forking in stable theories. Since then,
other tree properties have appeared and, together, these combinatorial
dividing lines (TP, TP1/SOP2, TP2,
SOP1, etc.) serve as the basis for a growing body of research in
model theory. I'll survey the work done in this area (and try to justify the
idea that it can be understood as an area) by explaining three of the core
ingredients in the theory developed so far: generalized indiscernibles,
dividing at a generic scale, and amalgamation.
- 9/1/2020 3PM (Midwest Computability Seminar),
University of California-Berkeley
Title: Part 1 of Martin's Conjecture for order
Abstract: Martin's Conjecture is an attempt to make precise the idea that the
only natural functions on the Turing degrees are the constant functions,
the identity, and transfinite iterates of the Turing jump. The conjecture is
typically divided into two parts. Very roughly, the first part states that
every natural function on the Turing degrees is either eventually constant
or eventually increasing and the second part states that the natural functions
which are increasing form a well-order under eventual domination, where the
successor operation in this well-order is the Turing jump.
In the 1980's, Slaman and Steel proved that the second part of Martin's
Conjecture holds for order-preserving Borel functions. In joint work with
Benny Siskind, we prove the complementary result that (assuming analytic
determinacy) the first part of the conjecture also holds for order-preserving
Borel functions (and under AD, for all order-preserving functions).
Our methods also yield several other new results, including an equivalence
between the first part of Martin's Conjecture and a statement about the
Rudin-Keisler order on ultrafilters on the Turing degrees.
In my talk, I will give an overview of Martin's Conjecture and then describe
our new results.
- 9/8/2020 3PM (Midwester Model Theory Seminar),
Western Illinois University, Macomb (visiting University of Vienna, Austria)
Title: Quantifier elimination for o-minimal groups
expanded by a valuational cut
Abstract: We let R be an o-minimal expansion of a group in a language in which
Th(R) eliminates quantifiers, and we let C be a valuational cut in R. We show
that if nonforking in certain Morley sequences is symmetric, then the theory
of R expanded by a predicate for C and a small number of constants eliminates
quantifiers. This is a generalization of results on o-minimal fields with
convex subrings satisfying some extra conditions such as T-convexity or
o-minimality of the residue field. This is joint work with C. F. Ealy.
- 9/15/2020 3PM (Midwest Computability Seminar),
University of Notre Dame, Indiana
Title: Noncomputable coding, density, and
Abstract: We introduce the
operations in order to construct sets of arbitrary intrinsic density from any
Martin-Löf random. We then show that these operations are useful more
generally for working with other notions of density as well, in particular,
for viewing Church and MWC stochasticity as a form of density.
- 9/22/2020 3PM (local UW logic seminar),
University of Lyon 1, France
Title: Invariant measures on the space of linear
orders on an ℵ0-categorical structure
Abstract: Let M be an ℵ0-categorical structure and denote by
LO(M) the compact space of linear orders on M. We investigate the probability
measures on LO(M) invariant under the natural action of the automorphism
group of M and prove, under rather general model-theoretic assumptions,
that either M has a definable linear order or LO(M) carries a unique
invariant measure (which can be easily and explicitly described). For
many structures M, the space LO(M) is the universal minimal flow of the
group Aut(M), and our work is in part motivated by a general unique
ergodicity question of Angel, Kechris, and Lyons in topological
dynamics. Our proof uses techniques from model theory, representation
theory, and probability theory, but no special knowledge will be assumed
in the talk. I will also provide some background and motivation. This is
joint work with Colin Jahel.
- 9/29/2020 3PM (Midwest Computability Seminar),
Drake University, Des Moines, Iowa
Title: Effective dimension and the intersection of
random closed sets
Abstract: The connection between the effective dimension of sequences and
membership in algorithmically random closed subsets of Cantor space was first
identified by Diamondstone and Kjos-Hanssen. In this talk, I highlight joint
work with Adam Case in which we extend Diamondstone and Kjos-Hanssen's result
by identifying a relationship between the effective dimension of a sequence
and what we refer to as the degree of intersectability of certain families of
random closed sets (also drawing on work by Cenzer and Weber on the
intersections of random closed sets).
As we show, (1) the number of relatively random closed sets that can have a
non-empty intersection varies depending on the choice of underlying probability
measure on the space of closed subsets of Cantor space - this number being the
degree of intersectability of a given family of random closed sets - and
(2) the effective dimension of a sequence X is inversely proportional to the
minimum degree of intersectability of a family of random closed sets, at least
one of which contains X as a member. Put more simply, a sequence of lower
dimension can only be in random closed sets with more branching, which are
thus more intersectable, whereas higher dimension sequences can be in random
closed sets with less branching, which are thus less intersectable, and the
relationship between these two quantities (that is, effective dimension and
degree of intersectability) can be given explicitly.
- 10/6/2020 3PM (local UW logic seminar),
Title: Complexity profiles and the generic Muchnik
Abstract: The generic Muchnik degrees, introduced by Schweber, give a way of
comparing the computability-theoretic content of uncountable structures.
Though obscured slightly by the need for some set-theoretic machinery, I hope
to highlight how this notion really gives an easy and natural way to talk
about computable structure theory for uncountable structures.
I will focus on the tool of complexity profiles.
Complexity profiles are a way of measuring, for two structures A generic
Muchnik reducible to B, which subsets of A can be defined using B.
The complexity profile of A on itself is the natural analog of considering
the relatively intrinsically Σksets in A.
Using complexity profiles, I will compare three generic muchnik degrees:
Cantor space < Baire space < the Borel-complete degree. In particular,
I will describe some dichotomy theorems regarding simple expansions of these
and describe how to build degrees strictly between them.
(Joint work with Joseph S. Miller, Noah Schweber, and Mariya Soskova.)
- 10/13/2020 3PM (Midwest Computability Seminar),
University of Warsaw, Poland
- 10/20/2020 3PM (Midwest Model Theory Seminar),
- 10/27/2020 3PM (Midwest Computability Seminar),
University of Notre Dame, Indiana
- 11/3/2020 3PM (local UW logic seminar),
University of Vienna, Austria
- 11/10/2020 3PM (Midwest Computability Seminar),
University of Leeds, England
- 11/17/2020 3PM (local UW logic seminar),
Jaap van Oosten,
Utrecht University, Netherlands
- 11/24/2020 3PM (Midwest Computability Seminar),
Wellesley College, Massachusetts
- 12/1/2020 3PM (local UW logic seminar),
University of Birmingham, England
- 12/8/2020 3PM (Midwest Computability Seminar),
Linda Brown Westrick,
Pennsylvania State University, State College
Archived UW Logic Seminar Pages