http://home.gwu.edu/~harizanv/Logic%20Seminar%20F09.html

10:30–11:30a.m.

Speaker: Rumen Dimitrov,
Western Illinois University

http://www.wiu.edu/users/rdd104/home.htm

Place: Rome Hall (801 22^{nd}
Street), Room 204

Title: *The age
of cohesive powers*

Abstract: Fra•ssˇ defined the age
of a structure *A* to be the class of
all structures isomorphic to the finitely generated substructures of *A*. He then used this term to refer to
one structure as being younger than another. In this talk, I will consider the
age of the rationals *Q* as a dense linear ordering without endpoints and as a field, and
will discuss connections with the earlier notion of the cohesive powers of *Q*. I will also establish different
model-theoretic properties of cohesive powers.

5:30–6:30p.m.

Speaker: Trang
Ha, GWU

Place:
Rome Hall (801 22^{nd} Street), Room 351

Abstract:**
**We consider
order relations on a computable magma. We discuss how these orders are represented
as infinite paths of a computable binary tree, while the Turing degrees are
preserved. Using the natural topology defined on the set of orders, we
investigate the topological properties of the space of orders. The lack of
computable orders leads to an interesting description of the space.

5:30–6:30p.m.

Speaker: Hakim Walker, GWU

Place:
Rome Hall (801 22^{nd} Street), Room 351

Abstract:**
**In 2014, Cenzer, Harizanov, and Remmel investigated computable injection structures,
two-to-one structures, and (2,0):1 structures, all of
which are types of infinite directed graphs derived from computable functions.
In this talk, we will define a (2,1):1 structure and
discuss various related computability-theoretic properties, including
branching, branch isomorphisms, computable categoricity, and relative computability categoricity.

5:30–6:30p.m.

Speaker: Valentina
Harizanov, GWU

Place:
Rome Hall (801 22^{nd} Street), Room 351

Abstract:**
**We will show how a set of natural
numbers can be coded into an order on a group. This will allows us to realize a
desired Turing degree, or even a strong degree, as the degree of an order on a
structure from a large class of groups.

4:00–5:00p.m.

Speaker: Michał Godziszewski, University of Warsaw and CUNY (Fulbright Research Scholar)

Place: Rome Hall (801 22^{nd} Street), Room 352

5:30–6:30p.m.

Speaker: Hakim Walker, GWU

Place:
Rome Hall (801 22^{nd} Street), Room 351

Abstract:**
**A
computable structure *M* is *computably categorical* if for every
computable copy *C* of *M,* there is a computable isomorphism
from *M* to *C*. Furthermore, a computable structure *M* is *relatively computably
categorical* if for every copy *B *of
*M,* there is an isomorphism computable
in the atomic diagram of *B*. Goncharov
showed that *M* is relatively
computably categorical if and only if *M*
has a *formally computably enumerable
Scott family*. Every relatively computably categorical structure is also
computably categorical, but the converse does not hold. We will present the
construction of a directed graph that is computably categorical but not
relatively so, by demonstrating the technique of diagonalizing
against Scott families.

**Special ****Colloquium**

__https://math.columbian.gwu.edu/colloquia__

**Friday, February 24, 2017**

1:30–2:30pm

Speaker: William Boney, Harvard University

Place: MPA (805 21st St NW), Room 305

Title:** ***Making nonelementary classes more elementary *

Abstract: Classification theory seeks
to organize classes of structures (such as algebraically closed fields, random
graphs, dense linear orders) along dividing lines that separate classes into well-behaved on one side and chaotic on the
other. Since its beginning, classification theory has discovered a
plethora of dividing lines for classes axiomatizable
in first-order logic and has been applied to solve problems in algebraic
geometry, topological dynamics, and more.

However, when looking at examining nonelementary classes (such as rank 1 valued fields or pseudoexponentiation), the lack of compactness is a serious
impediment to developing this theory. In the past decade, Grossberg and VanDieren have
isolated the notion of tameness. Tameness can be seen as a fragment of
compactness that is strong enough to allow the construction of classification
theory, but weak enough to be enjoyed by many natural examples. We will discuss
the motivation for classification theory in nonelementary
classes and some recent results using tameness, focusing on illuminating
examples.

**Special ****Colloquium**

__https://math.columbian.gwu.edu/colloquia__

**Thursday,
February 23, 2017**

1:30–2:30pm

Speaker: James Freitag, University of Illinois at Chicago

Place: Phillips Hall (801 22^{nd} Street), Room 217

Title:** ***Model theory and Painlevˇ equations*

5:30–6:30p.m.

Speaker: Valentina
Harizanov, GWU

http://home.gwu.edu/~harizanv/

Place:
Rome Hall (801 22^{nd} Street), Room 351

5:30–6:30p.m.

Speaker: Valentina
Harizanov, GWU

http://home.gwu.edu/~harizanv/

Place:
Rome Hall (801 22^{nd} Street), Room 351

5:20–6:20p.m.

Speaker: Wesley Calvert, Southern Illinois University

http://math.siu.edu/faculty-staff/faculty/calvert.php

Place:
Rome Hall (801 22^{nd} Street), Room 205

5:20–6:20p.m.

Speaker: Timothy McNicholl,
Iowa State University

https://sites.google.com/site/timothymcnicholl/

Place:
Rome Hall (801 22^{nd} Street), Room 205

Abstract: It is well known that many
algorithms that have very bad worst-case behavior work well in practice.
This has lead to the consideration of average-case behavior. However,
average-case behavior is often very difficult to calculate. This has led
to the consideration of efficient algorithms that fail only on a set of
asymptotic density 0; such an algorithm is said to compute coarsely.
Recently, coarse computability has been a topic of study in computability
theory, and a number of interesting connections to important
computability-theoretic concepts such as algorithmic randomness and genericity
have been discovered. I will discuss the basic definitions and results as
well as some open problems.

**Math
Colloquium**

**Friday, November 11****, 2016**

1:00–2:00pm

Speaker: Timothy McNicholl,
Iowa State University

https://sites.google.com/site/timothymcnicholl/

Place:
Rome Hall (801 22^{nd} Street), Room 206

Abstract: Computability theory is the mathematical study of the limits and potentialities of discrete computing devices. Computable analysis is the theory of computing with continuous data such as real numbers. Computable structure theory examines which computability-theoretic properties are possessed by the structures in various classes such as partial orders, Abelian groups, and Boolean algebras. Until recently computable structure theory has focused on classes of countable algebraic structures and has neglected the uncountable structures that occur in analysis such as metric spaces and Banach spaces. However, a program has now emerged to use computable analysis to broaden the purview of computable structure theory so as to include analytic structures. The solutions of some of the resulting problems have involved a delicate blend of methods from functional analysis and classical computability theory. We will discuss progress so far on metric spaces and Banach spaces, in particular $ell^p$ spaces, as well as open problems and new areas for investigation.

3:00–4:00p.m.

Speaker: Iva Bilanovic,
GWU

Place:
Philips Hall (801 22^{nd} Street), Room
736

Abstract: W will consider the computability-theoretic
complexity of finding a basis for a computable free group of infinite rank. We
will use basic properties of free groups to build a computable sequence of
computable infinitary ¹-2 formulas expressing the
property of membership in a basis. The relativized
limit lemma and these formulas will lead us to a ¹-2 basis.

5:30–6:30p.m.

Speaker: Jozef Przytycki,
GWU

http://home.gwu.edu/~przytyck/

Place:
Rome Hall (801 22^{nd} Street), Room 771

Abstract: The motivation for my talk
and related research comes from the confluence of two fascinating recent
developments: Khovanov homology in knot theory

and homological algebra and pseudo-knots in RNA folding theory in computational
biology.