ILLC-LIRa April 2024

illc-lira@list.uva.nl

1 participants
5 discussions

CHANGE: room L3.33 in Lab 42 for LIRa session: Hans van Ditmarsch (today, 16:30)
by LIRa Seminar 18 Apr '24

18 Apr '24

Dear all, Please note: The room for the LIRa session today had to be changed. *We will be in room L3.33 in Lab 42.* To attend online, please use our recurring zoom link: https://uva-live.zoom.us/j/89230639823?pwd=YWJuSnJmTDhXcWhmd1ZkeG5zb0o5UT09 (Meeting ID: 892 3063 9823, Passcode: 421723) You can find the details of the talk below. Speaker: Hans van Ditmarsch (University of Toulouse, CNRS, IRIT) Date and Time: Thursday, April 18th 2024, 16:30-18:00 Venue: room L3.33 in Lab 42 and online. Title: Distributed Knowledge Revisited. Abstract. We review the history and some recent work on what is known since the 1990s as distributed knowledge. Such epistemic group notions are currently getting more and more attention both from the modal logical community and from distributed computing, in various settings with communicating processes or agents. The typical intuition is that if a knows p, and b knows that p implies q, then together they know that q: they have distributed knowledge of q. In order to get to know q they need to share their knowledge. We will discuss: (i) the complete axiomatization, (ii) why not everything that is distributed knowledge can become common knowledge, (iii) the notion of collective bisimulation, (iv) distributed knowledge for infinitely many agents, (v) the novel update called resolving distributed knowledge and some variations (and its incomparable update expressivity to action models), (vi) distributed knowledge that is stronger than the sum of individual knowledge (where the relation for the group of agents is strictly contained in their intersection), (vii) common distributed knowledge and its topological interpretations, (viii) dynamic distributed knowledge, a version of the semantics ensuring that what is distributed knowledge becomes common knowledge, and the axiomatization, expressivity and bisimulation characterization of this logic. Hope to see you there! The LIRa team

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LIRa session: Hans van Ditmarsch (tomorrow, Thursday, 18 April 16:30)
by LIRa Seminar 17 Apr '24

17 Apr '24

Dear all, We will have our next LIRa session tomorrow, on Thursday, 18 April 16:30. To attend online, please use our recurring zoom link: https://uva-live.zoom.us/j/89230639823?pwd=YWJuSnJmTDhXcWhmd1ZkeG5zb0o5UT09 (Meeting ID: 892 3063 9823, Passcode: 421723) You can find the details of the talk below. Speaker: Hans van Ditmarsch (University of Toulouse, CNRS, IRIT) Date and Time: Thursday, April 18th 2024, 16:30-18:00 Venue: ILLC seminar room F1.15 in Science Park 107 and online. Title: Distributed Knowledge Revisited. Abstract. We review the history and some recent work on what is known since the 1990s as distributed knowledge. Such epistemic group notions are currently getting more and more attention both from the modal logical community and from distributed computing, in various settings with communicating processes or agents. The typical intuition is that if a knows p, and b knows that p implies q, then together they know that q: they have distributed knowledge of q. In order to get to know q they need to share their knowledge. We will discuss: (i) the complete axiomatization, (ii) why not everything that is distributed knowledge can become common knowledge, (iii) the notion of collective bisimulation, (iv) distributed knowledge for infinitely many agents, (v) the novel update called resolving distributed knowledge and some variations (and its incomparable update expressivity to action models), (vi) distributed knowledge that is stronger than the sum of individual knowledge (where the relation for the group of agents is strictly contained in their intersection), (vii) common distributed knowledge and its topological interpretations, (viii) dynamic distributed knowledge, a version of the semantics ensuring that what is distributed knowledge becomes common knowledge, and the axiomatization, expressivity and bisimulation characterization of this logic. Hope to see you there! The LIRa team

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LIRa session: Hans van Ditmarsch (Thursday, 18 April 16:30)
by LIRa Seminar 12 Apr '24

12 Apr '24

Dear all, We will have our next LIRa session on Thursday, 18 April 16:30. To attend online, please use our recurring zoom link: https://uva-live.zoom.us/j/89230639823?pwd=YWJuSnJmTDhXcWhmd1ZkeG5zb0o5UT09 (Meeting ID: 892 3063 9823, Passcode: 421723) You can find the details of the talk below. Speaker: Hans van Ditmarsch (University of Toulouse, CNRS, IRIT) Date and Time: Thursday, April 18th 2024, 16:30-18:00 Venue: ILLC seminar room F1.15 in Science Park 107 and online. Title: Distributed Knowledge Revisited. Abstract. We review the history and some recent work on what is known since the 1990s as distributed knowledge. Such epistemic group notions are currently getting more and more attention both from the modal logical community and from distributed computing, in various settings with communicating processes or agents. The typical intuition is that if a knows p, and b knows that p implies q, then together they know that q: they have distributed knowledge of q. In order to get to know q they need to share their knowledge. We will discuss: (i) the complete axiomatization, (ii) why not everything that is distributed knowledge can become common knowledge, (iii) the notion of collective bisimulation, (iv) distributed knowledge for infinitely many agents, (v) the novel update called resolving distributed knowledge and some variations (and its incomparable update expressivity to action models), (vi) distributed knowledge that is stronger than the sum of individual knowledge (where the relation for the group of agents is strictly contained in their intersection), (vii) common distributed knowledge and its topological interpretations, (viii) dynamic distributed knowledge, a version of the semantics ensuring that what is distributed knowledge becomes common knowledge, and the axiomatization, expressivity and bisimulation characterization of this logic. Hope to see you there! The LIRa team

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LIRa session: Alexandru Baltag (tomorrow, Thursday, 11 April 17:00)
by LIRa Seminar 10 Apr '24

10 Apr '24

Dear all, We will have our next LIRa session tomorrow, on Thursday, 11 April 17:00. To attend online, please use our recurring zoom link: https://uva-live.zoom.us/j/89230639823?pwd=YWJuSnJmTDhXcWhmd1ZkeG5zb0o5UT09 (Meeting ID: 892 3063 9823, Passcode: 421723) You can find the details of the talk below. Speaker: Alexandru Baltag (ILLC, Amsterdam) Date and Time: Thursday, April 11th 2024, 17:00-18:30 (note unusual time!) Venue: F1.15 and online. Title: Simple Recursion Laws for DEL and its extensions Abstract. There are two standard approaches to axiomatizing full DEL (with common knowledge and arbitrary events): (a) directly axiomatizing the dynamic logic, using ``Dynamic Induction" rules; and (b) extending the static base to Epistemic PDL (E-PDL) and reducing DEL to it using Recursion/Reduction axioms. Each of these options has its disadvantage: option (a) uses rather complex and non-standard rules, and the completeness proof is rather convoluted; while (b) uses a simple logic with a well-known axiomatization for the static logic, but the dynamic recursion/reduction axioms are extremely complex and opaque (-indeed, they take several pages of notations just to state). The same dilemma occurs again when DEL is extended to data-exchange events, in which agents access other agents' full information database: in the case, the relevant static base is Group Epistemic PDL (GE-PDL, i.e. PDL built on top of distributed knowledge modalities for groups of agents), but the relevant recursion laws become even more impenetrable. In this talk, I take a fresh look at the minimal static base needed for obtaining reductions for DEL and its mentioned extensions. By looking at recursion axioms as systems of equations, we are lead to extend the static language with polyadic conditionals, that are obtained as solutions to such systems of equations. Epistemically, these polyadic modalities capture various complex levels of conditional group knowledge, so they can be considered as generalizations of the common knowledge operator. As such, they can be given a transparent axiomatization and a filtration-based completeness proof, obtained by generalizing the corresponding axioms and proof for common knowledge. More importantly, the recursion/reduction laws become extremely simple and elegant. Even better, the same program can be applied to the extension of DEL with data-exchange events. This talk is based on joint work: reference [1], joint with Johan van Benthem; and [2], joint with Sonja Smets; and it also relates to older joint work [3]. REFERENCES: [1] A. Baltag & J. van Benthem: Updates, Generalized p-Morphisms, and (Co-)Recursive Equations. In J. van Benthem & F. Liu (eds), *Graph Games and Logic Design - Recent developments and further directions*, Springer 2024 to appear. [2] A. Baltag & S. Smets: Logics for Data Exchange and Communication. Submitted to AiML 2024. [3] A. Baltag and S. Smets: Learning what Others Know. In L. Kovacs and E. Albert (eds.), *LPAR23 proceedings of the International Conference on Logic for Programming AI and Reasoning*, EPiC Series in Computing, Volume 73, pp 90-110, 2020. https://doi.org/10.29007/plm4 Hope to see you there! The LIRa team

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LIRa session: Alexandru Baltag (Thursday, 11 April 17:00 - unusual time - on location and online)
by LIRa Seminar 05 Apr '24

05 Apr '24

Dear all, We will have our next LIRa session on Thursday, 11 April 17:00. This session will be on location and online. To attend via zoom please use our recurring link: https://uva-live.zoom.us/j/89230639823?pwd=YWJuSnJmTDhXcWhmd1ZkeG5zb0o5UT09 (Meeting ID: 892 3063 9823, Passcode: 421723) You can find the details of the talk below. Speaker: Alexandru Baltag (ILLC, Amsterdam) Date and Time: Thursday, April 11th 2024, 17:00-18:30 (note the unusual time!) Venue: F1.15 and online. Title: Simple Recursion Laws for DEL and its extensions Abstract. There are two standard approaches to axiomatizing full DEL (with common knowledge and arbitrary events): (a) directly axiomatizing the dynamic logic, using ``Dynamic Induction" rules; and (b) extending the static base to Epistemic PDL (E-PDL) and reducing DEL to it using Recursion/Reduction axioms. Each of these options has its disadvantage: option (a) uses rather complex and non-standard rules, and the completeness proof is rather convoluted; while (b) uses a simple logic with a well-known axiomatization for the static logic, but the dynamic recursion/reduction axioms are extremely complex and opaque (-indeed, they take several pages of notations just to state). The same dilemma occurs again when DEL is extended to data-exchange events, in which agents access other agents' full information database: in the case, the relevant static base is Group Epistemic PDL (GE-PDL, i.e. PDL built on top of distributed knowledge modalities for groups of agents), but the relevant recursion laws become even more impenetrable. In this talk, I take a fresh look at the minimal static base needed for obtaining reductions for DEL and its mentioned extensions. By looking at recursion axioms as systems of equations, we are lead to extend the static language with polyadic conditionals, that are obtained as solutions to such systems of equations. Epistemically, these polyadic modalities capture various complex levels of conditional group knowledge, so they can be considered as generalizations of the common knowledge operator. As such, they can be given a transparent axiomatization and a filtration-based completeness proof, obtained by generalizing the corresponding axioms and proof for common knowledge. More importantly, the recursion/reduction laws become extremely simple and elegant. Even better, the same program can be applied to the extension of DEL with data-exchange events. This talk is based on joint work: reference [1], joint with Johan van Benthem; and [2], joint with Sonja Smets; and it also relates to older joint work [3]. REFERENCES: [1] A. Baltag & J. van Benthem: Updates, Generalized p-Morphisms, and (Co-)Recursive Equations. In J. van Benthem & F. Liu (eds), *Graph Games and Logic Design - Recent developments and further directions*, Springer 2024 to appear. [2] A. Baltag & S. Smets: Logics for Data Exchange and Communication. Submitted to AiML 2024. [3] A. Baltag and S. Smets: Learning what Others Know. In L. Kovacs and E. Albert (eds.), *LPAR23 proceedings of the International Conference on Logic for Programming AI and Reasoning*, EPiC Series in Computing, Volume 73, pp 90-110, 2020. https://doi.org/10.29007/plm4 Hope to see you there! The LIRa team

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ILLC-LIRa April 2024