# This Week in Logic at CUNY

NOTE: the Seminar in Logic and Games meeting this Friday will be in room 4419.

Models of PA
Wednesday, October 30, 2013 6:30 pm GC 4214.03

Speaker: Erez Shochat St. Francis College
Title: Schmerl’s Lemma and Boundedly Saturated Models II

Set theory seminar
Friday, November 1, 2013 10:00 am GC 6417
Speaker: Karel Hrbacek City College of New York, CUNY
Title: Some problems motivated by nonstandard set theory
Link: http://nylogic.org/talks/some-problems-motivated-by-nonstandard-set-theoryNonstandard set theory enriches the usual set theory by a unary “standardness” predicate.  Investigations of its foundations raise a number of questions that can be formulated in ZFC or GB and appear open.  I will discuss several such problems concerning elementary embeddings, ultraproducts, ultrafilters and large cardinals.

Model theory seminar
Friday, November 1, 2013 12:30 pm GC6417
Speaker: David Lippel Haverford College
Title: Reverse VC calculations
Link: http://nylogic.org/talks/tba-6Let F be a family of sets, for example, a uniformly definable semi-algebraic family in real or p-adic n-space. The Vapnik-Chervonenkis (VC) dimension of F is a measurement of the combinatorial complexity of F. Once you know the VC dimension of F, theorems from computational geometry, like the Epsilon-Net Theorem, give nice geometric consequences for F. I will discuss a statistical strategy for reversing the flow of information in this theorem. Instead of starting with knowledge of the VC dimension, we merely hypothesize “dimension=d” for some value d. Then, we observe the geometric behavior of F using computer experiments and compare the observed behavior with the behavior that is predicted by the theorem (under the hypothesis “dimension=d”). If our observed results have sufficiently low probability (conditioned on “dimension=d”), then we can reject the hypothesis “dimension=d” with a high degree of confidence. Ultimately, we hope to use such methods to shed light on conjectures about VC density in the p-adics. This project is joint work with Deirdre Haskell and Nigel Pynn-Coates.

CUNY Logic Workshop
Friday, November 1, 2013 2:00 pm GC 6417
Speaker: Cameron Donnay Hill Department of Mathematics and Computer Science, Wesleyan University
Title: Category, Measure, and Expansions of Countably Categorical Structures
Link: http://nylogic.org/talks/cameron-hillA natural way to approach expansions of a fixed countably-categorical structure is through the compact metric space such expansions. In this talk, I will discuss some ways to recover “typical” but constrained expansions of a fixed structure from the points of view of measure and category. Regarding measure, I will discuss a slight generalization, and a new proof, of a result of Ackerman-Freer-Patel on concentrating invariant measures on the isomorphism type of a structure. And for category, I will discuss using certain kinds of ultrafilters to extract a “generic profile” of a given expansion. Time permitting, I will share some applications to zero-one laws, structural Ramsey theory, and/or regularity properties of definable graphs in finite fields.

Seminar in Logic and Games
Friday, November 1, 2013, 4:15 PM room 4410
Speaker: Eric Pacuit (University of Maryland)
Title: Dynamic Logics of Evidence Based Beliefs

Abstract:   The intuitive notion of evidence has both semantic and syntactic features. In this talk, I introduce and motivate an evidence logic for an  agents faced with possibly contradictory evidence from different sources. The logic is based on a neighborhood semantics, where a neighborhood N indicates that the agent has reason to believe that the true state of the world lies in N.    Further notions of relative plausibility between worlds and beliefs based on the ordering are then defined in terms of this evidence structure.    The semantics invites a number of natural special cases, depending on how uniform we make the  evidence sets, and how coherent their total structure. I will give an overview of the main axiomatizations for different classes of models and discuss logics that describe  the dynamics of changing evidence, and the resulting language extensions.   I will also discuss some intriguing connections  with logics of belief revision.
This is joint work with Johan van Benthem and David Fernandez-Duque.