ILLC-LIRa

illc-lira@list.uva.nl

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582 discussions

LIRa Session: Kees van Deemter
by LIRa Seminar 19 Apr '19

19 Apr '19

Dear all, The next LIRa session will take place on Thursday, April 25th. Please, find the details below: Speaker: Kees van Deemter (Utrecht University and University of Aberdeen) Date and Time: Thursday, April 25th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: The Elusive Benefits of Vagueness. Abstract. Much of everyday language is vague, yet the benefits of vagueness for hearers and readers are proving to be elusive. We discuss a range of earlier controlled experiments with human participants, and we report on a new series of experiments that we conducted in recent years. These new experiments, which focus on strategic use of vague expressions that are part of referential noun phrases, aim to separate the utility of vagueness (defined by the existence of borderline cases, as is common in theoretical work) from other factors that tend to co-occur with vagueness. Having presented the evidence, we argue that the evidence supports a view of vagueness where the benefits of vague terms are due to other influences, rather than to vagueness itself. These factors include: low granularity; the use of evaluative words; the avoidance of overtly numerical words; the existence of comparison strategies; and, lastly and more tentatively, a phenomenon that we call range reduction. Although it is possible that other types of vague expressions (i.e., outside referential noun phrases) behave differently, our work suggests that vagueness itself may not increase the utility of an expression at all. This is joint work with Matthew Green (Bournemouth University). Hope to see you there! The LIRa team

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Joint LIRa-Algebra|Coalgebra Session: Valentin Goranko
by LIRa Seminar 16 Apr '19

16 Apr '19

Dear all, *Tomorrow* we will have our next LIRa session, joint with the Algebra|Coalgebra seminar. Please find the details below: Speaker: Valentin Goranko (Stockholm University) Date and Time: Wednesday, April 17th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Towards a Logic for Conditional Strategic Reasoning. Abstract. This talk is based on a work in progress, joint with Fengkui Ju, Beijing Normal University. We consider systems of rational agents who act in pursuit of their individual and collective objectives and we study the reasoning of an agent or an external observer about the consequences from the expected choices of action of the other agents, based on their objectives, in order to assess the agent’s ability to achieve her own objective. For instance, consider a scenario where an agent, Alice, has an objective O(A) to achieve. Suppose, that Alice has several possible choices of an action (or, strategy) that would possibly, or certainly, guarantee the achievement of her objective O(A). Now, Bob, another agent or an external observer, is reasoning about the consequences from Alice\'s possible actions with respect to the occurrence of Bob’s objective or intended outcome O(B). Depending on Bob\'s knowledge about Alice\'s objective and of her available strategic choices that would guarantee the achievement of that objective, there can be several possible cases for Bob\'s reasoning, based on whether or not Bob knows Alice’s objective, her possible actions towards achieving that objective, and her intentions on how to act. Thus, Bob has to reason about his own abilities to achieve his objective O(B), conditional on what he knows or expect that Alice may decide to do. That scenario naturally extends to several agents reasoning about their abilities conditional on how they expect the others to act. In some of these cases, reasoning about conditional strategic abilities can be formally described in Coalition Logic (CL) or in its temporal extension, the alternating time temporal logic ATL(*), with semantics involving strategy contexts. Other cases, however, require new and more expressive operators capturing more refined patterns of strategic ability, especially suited for the kind of conditional strategic reasoning in scenarios described above. In our work we introduce and study such new operators and logical languages that can capture variations of conditional strategic reasoning. In this talk, after an informal discussion of conditional strategic reasoning, I will introduce some new strategic operators capturing such reasoning, will provide formal semantics for the resulting logical languages and will discuss briefly their expressiveness and some of their meta-properties. I will conclude with some open questions for future research. Hope to see you there! The LIRa team

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Correction on day
by LIRa Seminar 12 Apr '19

12 Apr '19

Dear all, Due to a mistake in the beginning of the previous e-mail: we emphasize that the next session, on the 17th of April (16:30-18:00) takes place on a *Wednesday*, and not on our regular Thursday slot. The LIRa team

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Joint LIRa-Algebra|Coalgebra Session: Valentin Goranko
by LIRa Seminar 12 Apr '19

12 Apr '19

Dear all, The next LIRa session (joint with the Algebra|Coalgebra seminar) will take place on Thursday, April 17th. Please, find the details below: Speaker: Valentin Goranko (Stockholm University) Date and Time: Wednesday, April 17th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Towards a Logic for Conditional Strategic Reasoning. Abstract. This talk is based on a work in progress, joint with Fengkui Ju, Beijing Normal University. We consider systems of rational agents who act in pursuit of their individual and collective objectives and we study the reasoning of an agent or an external observer about the consequences from the expected choices of action of the other agents, based on their objectives, in order to assess the agent’s ability to achieve her own objective. For instance, consider a scenario where an agent, Alice, has an objective O(A) to achieve. Suppose, that Alice has several possible choices of an action (or, strategy) that would possibly, or certainly, guarantee the achievement of her objective O(A). Now, Bob, another agent or an external observer, is reasoning about the consequences from Alice\'s possible actions with respect to the occurrence of Bob’s objective or intended outcome O(B). Depending on Bob\'s knowledge about Alice\'s objective and of her available strategic choices that would guarantee the achievement of that objective, there can be several possible cases for Bob\'s reasoning, based on whether or not Bob knows Alice’s objective, her possible actions towards achieving that objective, and her intentions on how to act. Thus, Bob has to reason about his own abilities to achieve his objective O(B), conditional on what he knows or expect that Alice may decide to do. That scenario naturally extends to several agents reasoning about their abilities conditional on how they expect the others to act. In some of these cases, reasoning about conditional strategic abilities can be formally described in Coalition Logic (CL) or in its temporal extension, the alternating time temporal logic ATL(*), with semantics involving strategy contexts. Other cases, however, require new and more expressive operators capturing more refined patterns of strategic ability, especially suited for the kind of conditional strategic reasoning in scenarios described above. In our work we introduce and study such new operators and logical languages that can capture variations of conditional strategic reasoning. In this talk, after an informal discussion of conditional strategic reasoning, I will introduce some new strategic operators capturing such reasoning, will provide formal semantics for the resulting logical languages and will discuss briefly their expressiveness and some of their meta-properties. I will conclude with some open questions for future research. Hope to see you there! The LIRa team

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LIRa Session: Ana Lucia Vargas Sandoval
by LIRa Seminar 10 Apr '19

10 Apr '19

Dear all, Tomorrow we will have our next LIRa session. Please, find the details below: Speaker: Ana Lucia Vargas Sandoval (ILLC) Date and Time: Thursday, April 11th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: On the learning with positive and with complete data Abstract. In this talk, I will present a study that addresses the differences between learning (of classes of recursive sets of natural numbers) with positive and with complete information. In particular, concerning the framework of learning with certainty or finite identification. The difference between finite identification with positive (pfi) and with complete data (cfi), if not as huge as in the learning in the limit case, is considerable not only in power but also in character. As we will see, the structural properties and computational recursive ones bring out different flavours in this distinction. We will see that for finite families (finite classes of finite sets of natural numbers) the difference lies exactly in the fact that for positive identification the families need to be anti-chains, while in the infinite case it is less simple, being an anti-chain is no longer a sufficient condition. We will also address maximal learnable families, identifiable families with no proper extension which can be identified, first with positive information and then with complete information. We will see an example of a computable (non-canonical) anti-chain of finite languages which is not pfi and not cfi. Time permitting, we will address a conjecture of ours, namely that each pfi family has either finitely many or uncountably many maximal non-effective pfi extensions. We will finalise with some current questions we are entertaining and further ways to continue. Hope to see you there! The LIRa team

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LIRa Session: Ana Lucia Vargas Sandoval
by LIRa Seminar 05 Apr '19

05 Apr '19

Dear all, The next LIRa session will take place on Thursday, April 11th. Please, find the details below: Speaker: Ana Lucia Vargas Sandoval (ILLC) Date and Time: Thursday, April 11th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: On the learning with positive and with complete data Abstract. In this talk, I will present a study that addresses the differences between learning (of classes of recursive sets of natural numbers) with positive and with complete information. In particular, concerning the framework of learning with certainty or finite identification. The difference between finite identification with positive (pfi) and with complete data (cfi), if not as huge as in the learning in the limit case, is considerable not only in power but also in character. As we will see, the structural properties and computational recursive ones bring out different flavours in this distinction. We will see that for finite families (finite classes of finite sets of natural numbers) the difference lies exactly in the fact that for positive identification the families need to be anti-chains, while in the infinite case it is less simple, being an anti-chain is no longer a sufficient condition. We will also address maximal learnable families, identifiable families with no proper extension which can be identified, first with positive information and then with complete information. We will see an example of a computable (non-canonical) anti-chain of finite languages which is not pfi and not cfi. Time permitting, we will address a conjecture of ours, namely that each pfi family has either finitely many or uncountably many maximal non-effective pfi extensions. We will finalise with some current questions we are entertaining and further ways to continue. Hope to see you there! The LIRa team

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LIRa Session: Malvin Gattinger
by LIRa Seminar 03 Apr '19

03 Apr '19

Dear all, Tomorrow we will have our next LIRa session. Please, find the details below: Speaker: Malvin Gattinger (University of Groningen) Date and Time: Thursday, April 4th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Adding Boolean Definitions to Public Announcement Logic. Abstract. In standard epistemic logic, knowing p means to know that p is true, not saying anything about understanding p. In this talk I will present joint work with Yanjing Wang where we extend PAL to address this limitation. We define the meaning of propositions with boolean formulas and add an operator for `equivalence by definition\' to the language. We can then model agents with different knowledge or belief about both the truth value and the meaning of propositions. For example, an agent may understand a proposition without knowing its truth value or the other way round. Moreover, multiple agents might agree that something is true without agreeing on its meaning and vice versa. The talk will include various examples and a sketch of the completeness proof. It should be accessible to everyone with some background in epistemic logic. Hope to see you there! The LIRa team

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LIRa Session: Malvin Gattinger
by LIRa Seminar 29 Mar '19

29 Mar '19

Dear all, The next LIRa session will take place on Thursday, April 4th. Please, find the details below: Speaker: Malvin Gattinger (University of Groningen) Date and Time: Thursday, April 4th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Adding Boolean Definitions to Public Announcement Logic. Abstract. In standard epistemic logic, knowing p means to know that p is true, not saying anything about understanding p. In this talk I will present joint work with Yanjing Wang where we extend PAL to address this limitation. We define the meaning of propositions with boolean formulas and add an operator for `equivalence by definition\' to the language. We can then model agents with different knowledge or belief about both the truth value and the meaning of propositions. For example, an agent may understand a proposition without knowing its truth value or the other way round. Moreover, multiple agents might agree that something is true without agreeing on its meaning and vice versa. The talk will include various examples and a sketch of the completeness proof. It should be accessible to everyone with some background in epistemic logic. Hope to see you there! The LIRa team

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LIRa Session: Peter Hawke
by LIRa Seminar 27 Mar '19

27 Mar '19

Dear all, Tomorrow we will have our next LIRa session. Please, find the details below: Speaker: Peter Hawke (ILLC) Date and Time: Thursday, March 28th 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Logical Omniscience and Knowledge Per se. Abstract. I\'ll report on the latest developments in an ongoing project on the problem of logical omniscience, emphasizing recent technical developments (joint work with Aybuke Ozgun and Franz Berto). A problem of logical omniscience arises, roughly, when, relative to a class of agents, (i) one\'s theory of an epistemic attitude is committed to it being closed under logical implication, and (ii) this is, prima facie, a misrepresentation of that attitude. We concentrate on a fundamental version of the problem, concerning ordinary knowledge ascription (\'knowledge per se\') and arbitrary agents. Though logical omniscience is obviously problematic for a theory of knowledge per se, it is plausible that knowledge per se obeys some (static and dynamic) logical principles. We try to capture this with three complementary tools: (i) taking content as composed of truth conditions and topic; (ii) taking minds as fragmented; (iii) taking knowledge as defeasible. We compare our logical system to related ones and exhibit soundness and completeness results. Hope to see you there! The LIRa team

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LIRa Session: Fausto Barbero
by LIRa Seminar 19 Mar '19

19 Mar '19

Dear all, The next LIRa session will take place this Thursday. Our speaker is Fausto Barbero (and not Thomas Schindler, as was announced in the ILLC newsletter!). You can find more details on the talk below: Speaker: Fausto Barbero (University of Helsinki) Date and Time: Thursday, March 21st 2019, 16:30-18:00 Venue: ILLC Seminar Room F1.15, Science Park 107. Title: Interventionist Counterfactuals in Team Semantics. Abstract. Team semantics is a generalization of Tarskian semantics which allows the introduction of a greater variety of logical operators - most notably, atoms which express dependencies among variables. This extra degree of freedom is obtained by replacing the notion of satisfaction by an assignment with satisfaction by a set of assignments (\"team\"). I will show how to enrich this framework so that a notion of intervention (in the spirit of structural equation modeling) can be applied to teams. After this move, it becomes possible to introduce interventionist counterfactuals over teams, and express a variety of notions of causal dependence in terms of them. I will consider a basic formalism which conservatively extends the usual languages of causal modelling, and some further operators. Passing from teams to multiteams (multisets of assignments), we will see a way of introducing probabilities in the framework. It will emerge that some distinctions made in causal modelling, e.g. between \"do expressions\" and \"counterfactual expressions\", can be explained in terms of commutation of simpler logical operators. . Hope to see you there! The LIRa team

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