**Seminar in Logic and Games**

** Thursday, September 20, 2012, 1 PM to 2:30 PM, room 4421**

Choosing Products in Social Networks

Krzysztof R. Apt (CWI and University of Amsterdam)

Abstract: Social networks have become a huge interdisciplinary

research area with

important links to sociology, economics, epidemiology, computer

science, and mathematics.

We introduce a new threshold model of social networks, in which the

nodes influenced by their neighbours can adopt one out of several

alternatives (products).

We study various algorithmic questions concerning these networks, for

example the problem of computing the minimum (resp. maximum) possible

spread of a product.

Also, using game-theoretic concepts, we analyze the consequences of

adopting products by the agents who form the network. In particular,

we prove that determining an existence of a (pure) Nash equilibrium is

NP-complete.

We explain how these results can be used to analyze consequences

of the addition of new products to a social network. We show that in

some cases such an addition can permanently destroy market stability.

Based on joint works with Vangelis Markakis and Sunil Simon.

**Logic Workshop**

** Friday, September 21, 2012 2:00 pm GC 6417**

Professor Patricia Blanchette (Notre Dame University)

Logic and conceptual analysis in Frege

Abstract. Gottlob Frege understood logical entailment very differently

than did David Hilbert, and hence understood e.g. independence and

consistency in what now count as quite unorthodox ways. The purpose of

this talk is to explain the motivation for Frege’s conception, and to

investigate some of its implications for evaluating the importance of

e.g. the existence of models of theories, the completeness of

first-order logic, and related topics. I’ll argue that by coming to

understand Frege better, we gain a better understanding of the

historical trajectory that logic in fact followed, as contrasted with

the one that Frege would have pursued.

**The New York Philosophical Logic Group**

** Tuesday, Sep 25, 2012**

Speaker: Graham Priest (GC, CUNY)

Topic: Validity Curries

Time/Place: Tuesday Sept. 25, 7:15 p.m. to 9:15 p.m., 2nd floor seminar

room, NYU Philosophy Dept (5, Washington Place)

Brief Abstract: Curry Paradoxes involving truth and set-hood are well known.

Those who favour unrestricted truth predicates and abstraction principles,

have tended to solve the paradoxes by rejecting the principle of Contraction

for conditionals. Of late, paradoxes in the same family, but involving the

notion of validity, have been turning up; and it would appear that these

cannot be solved in this way. In this talk I will suggest how these may be

solved by deploying a sub-structural logic which rejects Contraction for

premises.