# This Week in Logic at CUNY

Computational Logic Seminar
November 13, Time 2:00 – 4:00 PM, GC Room 3309
Title: Applied higher infinities in impredicative constructive set theories.

Abstract: The Intuitionistic Zermelo Fraenkel set theory IZF was
introduced by Myhill more than 30 years ago, starting investigations
into the world of constructive set theories. I will give an overview
of this area and describe the recent results that apply inaccessible
sets to combine the proof-theoretical benefits of the version with
Replacement with the consistency power of the version with Collection.
Related open questions will be discussed.

Second Annual Saul Kripke Lecture
4:00-6:00 pm this Tuesday November 13, 2012, at CUNY Graduate Center,
Rooms C201 and C202
Speaker: John Burgess (John N. Woodhull Professor of Philosophy,
Princeton University)
Title: The Origin of Necessity and the Necessity of Origin

Please visit the Saul Kripke Center’s website for further information,
and to keep up with future events:
http://web.gc.cuny.edu/KripkeCenter/
If you have any questions, feel free to email us atkripkeconference@gc.cuny.edu

Set Theory Seminar
Friday, November 16, 2012, 10:00am GC 6417
Alexander Rapp
Diamond Plus and the Kurepa Hypothesis

Model Theory Seminar
Friday, November 16, 2012, 12:30pm-1:45pm, GC 6417
Lynn Scow (UIC)
Generalized Indiscernible Sets, Ehrenfeucht-Mostowski Types, Trees

Abstract: A generalized indiscernible set is a set of parameters $A = \{a_i : i \in I\}$ where the $a_i$ are finite tuples from a structure
$M$, $I$ is some additional structure, and $A$ satisfies a homogeneity
condition: finite tuples $(a_{i_1}, \ldots, a_{i_n}), (a_{j_1}, \ldots, a_{j_n})$ from $A$ have the same type in $M$, provided the
tuples of their indices, $(i_1,\ldots,i_n), (j_1,\ldots,j_n)$, have
the same quantifier-free type in $I$. Generalized indiscernible sets
were introduced by Shelah in the 70’s and have important applications
in classification theory. In this talk, I will extend the definition
of Ehrenfeucht-Mostowski type (EM-type) from order-indiscernible sets
to generalized indiscernible sets. The EM-type is a means to encode
the important first-order information in $A$, and it can be a useful
way to streamline compactness arguments. In this talk I will survey
the uses of EM-types, and as a consequence, present a new Ramsey class
of trees.

Logic Workshop
Friday, November 16, 2012 2:00 pm GC 6417
Prof. David Marker (University of Illinois – Chicago)
Integer parts of uncountable real closed fields

Abstract. An integer part of a real closed field is a discretely
ordered subring where every element of the field is within distance
one of an element of the ring. Shepherdson first noticed that integer
parts are models of a weak fragment of arithmetic. Recently, D’Aquino,
Knight and Starchenko studied the real closed fields where the integer
part is a model of Peano Arithmentic and gave a complete
classification in the countable case. We will survey the subject and
examine some phenomena in the uncountable case.

New York Logic Colloquium
November 16, Friday, 4-5:30pm
Speaker: Johan van Benthem (Professor of Logic, Amsterdam and Stanford
University. http://staff.science.uva.nl/~johan/)
Title: IMPLICIT AND EXPLICIT STANCES IN LOGIC

Abstract: We identify a pervasive contrast in modeling styles in
logic, between ‘implicit’ and ‘explicit’ approaches. Roughly speaking,
the former change the meaning of logical constants and consequence to
accommodate new topics entering the field, while the explicit approach
extends classical logical systems with new vocabulary.

We discuss the contrast in intuitionistic vs. epistemic logic, default
reasoning, logics of questions, information dynamics and games, and
then define the stances more sharply. Many new issues become visible
concerning dualities and merges between the two approaches. Finally,
in philosophical mode, we discuss what the contrast means for an
understanding of logic as a repertoire of natural stances.

References:
Johan van Benthem, 1991, ‘Implicit versus Explicit Views of
Knowledge’, Proceedings TARK. –
2009, ‘The Information in Intuitionistic Logic’, Synthese. –
2011, Logical Dynamics of Information and Interaction, Cambridge
University Press.

THE TALK WILL BE FOLLOWED BY A WINE AND CHEESE RECEPTION.