ILLC-LIRa

illc-lira@list.uva.nl

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LIRa Session: Karolina Krzyżanowska
by LIRa Seminar 24 Oct '18

24 Oct '18

Dear all, Tomorrow we will have our next LIRa session. Please, find the details below: Speaker: Karolina Krzyżanowska Date and Time: Thursday, October 25th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: True clauses and false connections: what’s wrong with missing-link conditionals? Abstract. The majority of the prominent theories of indicative conditionals validate the Principle of Conjunctive Sufficiency. That is, on those accounts, whenever the antecedent, P, and the consequent, Q, are true, the conditional, “If P then Q,” is acceptable, whether or not there is a meaningful connection between P and Q. At the same time, almost everyone seems to agree that conditionals without a connection are odd. Gricean explanation of the oddity of missing-link conditionals rests on an observation that such conditionals are rendered highly acceptable only in situations in which a stronger assertion, for instance, that of a conjunction of P and Q, is warranted. Asserting a weaker, less informative conditional is odd because it is a violation of the Maxim of Quantity. In my talk, I will present empirical data that challenge Gricean explanation of why missing-link conditionals are odd. Furthermore, I will argue that these findings can be reconciled with general principles of Gricean pragmatics, but at the cost of giving up Conjunctive Sufficiency. Hope to see you there! The LIRa team

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LIRa Session: Karolina Krzyżanowska
by LIRa Seminar 19 Oct '18

19 Oct '18

Dear all, The next LIRa session will take place on Thursday, October 25th . Our speaker is Karolina Krzyżanowska. Please, find the details below: Date and Time: Thursday, October 25th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: TBA. Abstract. TBA. Hope to see you there! The LIRa team

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LIRa Session: CANCELLED
by LIRa Seminar 10 Oct '18

10 Oct '18

Dear all, Unfortunately, there will be no LIRa session tomorrow because our speaker is ill. The LIRa team

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LIRa Session: Alexandru Baltag
by LIRa Seminar 10 Oct '18

10 Oct '18

Dear all, Tomorrow we will have our next LIRa session. Please, find the details below: Speaker: Alexandru Baltag Date and Time: Thursday, October 11th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: The Logic of Correlations. Abstract. I present a Logic of Correlations (LC), as an extension of the Epistemic Dependence Logic presented in my 2016 AiML paper, that essentially axiomatized a ``feasible\" version of Vaananen\'s Dependence Logic. The semantics extends van Benthem\'s Generalized-Assignment Semantics of First-Order Logic (on ``dependency models\"). While the usual semantics of FOL allows all possible assignments of variables to objects, a dependency model restricts the range of available assignments to a given subset. One can think of the available assignments as ``possible worlds\", and the FOL quantifiers become Kripke modalities. Dependency models were proposed as a model for capturing dependencies and correlations between variables: essentially, they are the same as the ``teams\" (sets of assignments) used in Hodges\' team semantics for Dependence Logic. This modal version of FOL is known to be decidable, but unfortunately it is so weak that it cannot actually express variable dependencies in an explicit manner (though the model still implicitly captures these dependencies). My Epistemic Dependence Logic proposed a remedy to this limitation, by adding an epistemic operator K_y x (x is knowable given y), that captures a \'local\' version of the so-called dependence atoms from Dependence Logic: all assignments (available in the model) that agree with the current assignment on y also agree with it on x. In this talk I generalize this further, by introducing accessibility relations R for informational ``links\" between assignments. A link is a finite relation between variables. Two assignments w and v are linked by the corresponding accessibility relation if for every pair (x,y) in the link we have w(x)=v(y). In other words, links capture commonality of objects between assignments: x denotes the same object in world w as the one denoted by y in world v. Correlations are dependencies between links, that express informational dependencies between them. LC can be of use in Computer Science to reason about functional dependencies in a database, but also in Physics to encode natural laws capturing causal correlations between physical variables, etc..Unlike Dependence Logic, LC is decidable. Time-permitting, I will try to sketch the main ideas behind the decidability proof (based on an elaboration of the quasi-model method pioneered by van Benthem, and closely related to the mosaic method of Andreka and Nemeti). . Hope to see you there! The LIRa team

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LIRa Session: Alexandru Baltag
by LIRa Seminar 05 Oct '18

05 Oct '18

Dear all, The next LIRa session will take place on Thursday, October 11th. Our speaker is Alexandru Baltag. Please, find the details below: Speaker: Alexandru Baltag Date and Time: Thursday, October 11th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: The Logic of Correlations Abstract: I present a Logic of Correlations (LC), as an extension of the Epistemic Dependence Logic presented in my 2016 AiML paper, that essentially axiomatized a \"feasible\" version of Vaananen\'s Dependence Logic. The semantics extends van Benthem\'s Generalized-Assignment Semantics of First-Order Logic (on \"dependency models\"). While the usual semantics of FOL allows all possible assignments of variables to objects, a dependency model restricts the range of available assignments to a given subset. One can think of the available assignments as ``possible worlds\", and the FOL quantifiers become Kripke modalities. Dependency models were proposed as a model for capturing dependencies and correlations between variables: essentially, they are the same as the \"teams\" (sets of assignments) used in Hodges\' team semantics for Dependence Logic. This modal version of FOL is known to be decidable, but unfortunately it is so weak that it cannot actually express variable dependencies in an explicit manner (though the model still implicitly captures these dependencies). My Epistemic Dependence Logic proposed a remedy to this limitation, by adding an epistemic operator K_y x (x is knowable given y), that captures a `local\' version of the so-called dependence atoms from Dependence Logic: all assignments (available in the model) that agree with the current assignment on y also agree with it on x. In this talk I generalize this further, by introducing accessibility relations R for informational \"links\" between assignments. A link is a finite relation between variables. Two assignments w and v are linked by the corresponding accessibility relation if for every pair (x,y) in the link we have w(x)=v(y). In other words, links capture commonality of objects between assignments: x denotes the same object in world w as the one denoted by y in world v. Correlations are dependencies between links, that express informational dependencies between them. LC can be of use in Computer Science to reason about functional dependencies in a database, but also in Physics to encode natural laws capturing causal correlations between physical variables, etc..Unlike Dependence Logic, LC is decidable. Time-permitting, I will try to sketch the main ideas behind the decidability proof (based on an elaboration of the quasi-model method pioneered by van Benthem, and closely related to the mosaic method of Andreka and Nemeti). Hope to see you there! The LIRa team

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DIP Colloquium this week
by LIRa Seminar 01 Oct '18

01 Oct '18

Dear all, As you might have noticed, there is no LIRa session this Thursday. Instead, we encourage you to attend the DIP Colloquium talk by Peter Gärdenfors. You can find the details below: Speaker: Peter Gärdenfors (Lund) Title: Where Do Semantic Domains Come From Date: Thursday 4 October 2018 Time: 11:00 - 12:30 Location: ILLC seminar room F1.15 Hope to see you there! The LIRa team

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LIRa Session: Zoi Terzopoulou
by LIRa Seminar 26 Sep '18

26 Sep '18

Dear all, Tomorrow we will have our next LIRa session. Please, find the details below: Speaker: Zoi Terzopoulou Date and Time: Thursday, September 27th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Aggregating Incomplete Pairwise Preferences by Weight. Abstract. Within the area of Computational Social Choice, we develop a model for the aggregation of preferences that do not need to be either complete or transitive. Our focus is on the normative characterisation of aggregation rules under which each agent has a weight that depends only on the size of her ballot, i.e., on the number of pairs of alternatives for which she chooses to report a relative ranking. We show that for rules that satisfy a restricted form of majoritarianism these weights in fact must be constant, while for rules that are invariant under agents with compatible preferences forming pre-election pacts it must be the case that an agent’s weight is inversely proportional to the size of her ballot. The talk is based on joint work with Ulle Endriss, and will not require any background on Computational Social Choice. Hope to see you there! The LIRa team

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LIRa Session: Zoi Terzopoulou
by LIRa Seminar 21 Sep '18

21 Sep '18

Dear all, The next LIRa session will take place on Thursday, September 27th. Our speaker is Zoi Terzopoulou. Please, find the details below: Speaker: Zoi Terzopoulou Date and Time: Thursday, September 27th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Aggregating Incomplete Pairwise Preferences by Weight. Abstract. Within the area of Computational Social Choice, we develop a model for the aggregation of preferences that do not need to be either complete or transitive. Our focus is on the normative characterisation of aggregation rules under which each agent has a weight that depends only on the size of her ballot, i.e., on the number of pairs of alternatives for which she chooses to report a relative ranking. We show that for rules that satisfy a restricted form of majoritarianism these weights in fact must be constant, while for rules that are invariant under agents with compatible preferences forming pre-election pacts it must be the case that an agent’s weight is inversely proportional to the size of her ballot. The talk is based on joint work with Ulle Endriss, and will not require any background on Computational Social Choice. Hope to see you there! The LIRa team

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LIRa Session: Gianluca Grilletti
by LIRa Seminar 19 Sep '18

19 Sep '18

Dear all, This is a reminder of tomorrow\'s LIRa session. Please, find the details below: Speaker: Gianluca Grilletti Date and Time: Thursday, September 20th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: An Ehrenfeucht-Fraïssé Game for InqBQ. Abstract. InqBQ [1] is a first-order version of inquisitive logic, encompassing both questions and quantifiers. Questions like ``What is an element with property P?’’ and ``What is the extension of property P?\'\' can be represented using the usual logical operators from first-order logic in addition to the inquisitive counterpart of classical disjunction and classical existential quantifier respectively. Several questions about InqBQ remain open: Is the entailment of the logic axiomatizable? Does the entailment between questions boil down to some dependency between the statements supporting the questions? Which questions are expressible and which are not expressible? Ehrenfeucht-Fraïssé games [2,4] proved to be a valuable tool to study the expressive power of several logics [3,5,8]. The main idea is to characterize logical equivalence between models, w.r.t. the whole logic or certain fragments of it, using game-theoretic tools; this in turn gives a strategy to prove that certain properties of models -- e.g. the finiteness of the domain in first-order logic -- are not expressible, namely by finding a winning strategy in a suitable game. In this talk I will present an EF-game for InqBQ and the corresponding characterization theorem. I will apply the result obtained to show that certain natural questions -- e.g. “How many elements have property P?” -- are not expressible by InqBQ formulas. (This is joint work with Ivano Ciardelli.) References [1] Ivano Ciardelli. Questions in logic. PhD thesis, Institute for Logic, Language and Computation, University of Amsterdam, 2016. [2] Andrzej Ehrenfeucht. An application of games to the completeness problem for formalized theories. Journal of Symbolic Logic, 32(2):281–282, 1967. [3] Ronald Fagin. Monadic Generalized Spectra. Zeitschrift für mathematische Logik und Grundlagen der Mathematik, 21:89–96, 1975. [4] Roland Fraïssé. Sur quelques classifications des systèmes de relations. Publications Scientifiques de l’Université D’Alger, 1(1):35–182, June 1954. [5] Neil Immerman. Upper and lower bounds for first order expressibility. Journal of Com- puter and System Sciences, 25(1):76–98, 1982. [6] Jouko Väänänen. Models and Games. Cambridge University Press, New York, NY, USA, 1st edition, 2011. Hope to see you there! The LIRa team

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LIRa Session: Gianluca Grilletti
by LIRa Seminar 14 Sep '18

14 Sep '18

Dear all, The next LIRa session will take place on Thursday, September 20th. Our speaker is Gianluca Grilletti. Please, find the details below: Speaker: Gianluca Grilletti Date and Time: Thursday, September 20th 2018, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: An Ehrenfeucht-Fraïssé Game for InqBQ. Abstract. InqBQ [1] is a first-order version of inquisitive logic, encompassing both questions and quantifiers. Questions like ``What is an element with property P?’’ and ``What is the extension of property P?\'\' can be represented using the usual logical operators from first-order logic in addition to the inquisitive counterpart of classical disjunction and classical existential quantifier respectively. Several questions about InqBQ remain open: Is the entailment of the logic axiomatizable? Does the entailment between questions boil down to some dependency between the statements supporting the questions? Which questions are expressible and which are not expressible? Ehrenfeucht-Fraïssé games [2,4] proved to be a valuable tool to study the expressive power of several logics [3,5,8]. The main idea is to characterize logical equivalence between models, w.r.t. the whole logic or certain fragments of it, using game-theoretic tools; this in turn gives a strategy to prove that certain properties of models -- e.g. the finiteness of the domain in first-order logic -- are not expressible, namely by finding a winning strategy in a suitable game. In this talk I will present an EF-game for InqBQ and the corresponding characterization theorem. I will apply the result obtained to show that certain natural questions -- e.g. “How many elements have property P?” -- are not expressible by InqBQ formulas. (This is joint work with Ivano Ciardelli.) References [1] Ivano Ciardelli. Questions in logic. PhD thesis, Institute for Logic, Language and Computation, University of Amsterdam, 2016. [2] Andrzej Ehrenfeucht. An application of games to the completeness problem for formalized theories. Journal of Symbolic Logic, 32(2):281–282, 1967. [3] Ronald Fagin. Monadic Generalized Spectra. Zeitschrift für mathematische Logik und Grundlagen der Mathematik, 21:89–96, 1975. [4] Roland Fraïssé. Sur quelques classifications des systèmes de relations. Publications Scientifiques de l’Université D’Alger, 1(1):35–182, June 1954. [5] Neil Immerman. Upper and lower bounds for first order expressibility. Journal of Com- puter and System Sciences, 25(1):76–98, 1982. [6] Jouko Väänänen. Models and Games. Cambridge University Press, New York, NY, USA, 1st edition, 2011. Hope to see you there! The LIRa team

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