Supergroup BLAST!
Shay Logan
Dear Cheerful Logicians and Friends of Logic,
Supergroup announcement time! Brief Summary: There are two talks to announce, both on Thursday. First is Alejandra Diaz-Caro talking about Extensional Proofs. Second is the supergroup talk, featuring Sophia Knight, who will talk about strategy logic. Details follow.
Supergroup Talk:
Speaker: Sophia Knight
Title: Some work on strategy logic with imperfect information
Time and Date: Thursday, July 23, 8 pm GMT-5
Link: https://unimelb.zoom.us/j/846890369?pwd=TktZYmlIUGlYOU9ZaXFJcCt0TFJFZz09
Abstract: There is a great deal of work on logics for games in multi-agent systems. These logics are concerned with formally defining statements like "If Alice and Bob cooperate, they can follow a strategy so that they are certain to achieve their goal," or "no matter what Cath does, she cannot be sure of achieving her goal," or "Alice can ensure that either Bob is certain not to reach his goal, no matter what he does, or Cath is cerain to reach her goal if she follows the right strategy." My talk will be focused on how to include imperfect information in these systems: if the agents do not have full information about the current state of the system, how does this change their power to act strategically in order to achieve their goals? In particular, I will discuss my current work with Bastien Maubert on some approaches to the formal expression of agents' knowledge and strategic abilities in multi-agent systems with imperfect information.
I will begin by presenting Alternating-time Temporal Logic (ATL), a logic describing the abilities of coalitions of agents in concurrent game structures. I will describe some difficulties with adapting variants of ATL to imperfect information settings. Next I will introduce Strategy Logic (SL), a logic with a similar purpose to ATL, which differs in that it takes strategies to be explicit objects in the logic, making it more powerful but less decidable than ATL. For example, SL can state the existence of Nash equilibria, whereas ATL cannot. I will describe our current work on an imperfect information variant of SL, the addition of epistemic operators, the difficulties in restricting SL to only consider uniform strategies, and a solution to this difficulty.
Talks by Member Groups:
Lógicos em Quarentena (SBL)
Speaker: Alejandro Diaz-Caro
Title: Extensional proofs in a propositional logic modulo isomorphisms
Time and Date: Thursday, July 23, 4pm GMT-3
Link: https://meet.google.com/keg-nezd-dnz
Abstract: Joint work with Gilles Dowek. System I is a proof language for a fragment of propositional logic where isomorphic propositions, such as A∧B and B∧A, or A⇒(B∧C) and (A⇒B)∧(A⇒C) are made equal. System I enjoys the strong normalization property. This is sufficient to prove the existence of empty types, but not to prove the introduction property (every normal closed term is an introduction). Moreover, a severe restriction had to be made on the types of the variables in order to obtain the existence of empty types. We show here that adding η-expansion rules to System I permit to drop this restriction and to retrieve full introduction property. Preprint at arXiv.org:2002.03762.
Other Notes and Announcements:
The Logic Supergroup has a YouTube channel! Recordings of almost all talks are available at https://www.youtube.com/channel/UCqOAS8SHP-5nGjYEE2FE6xw
To access the supergroup calendar, please follow this link: https://calendar.google.com/calendar?cid=ZGhoanNoanF1bGhmaG9xam5scDJlc2o0bDhAZ3JvdXAuY2FsZW5kYXIuZ29vZ2xlLmNvbQ
To access the member groups joint calendar, please follow this link: https://calendar.google.com/calendar?cid=aG8wNWljaGxkNXI2N2oyMnZvY3BzdmRoMWNAZ3JvdXAuY2FsZW5kYXIuZ29vZ2xlLmNvbQ
If you represent a member group and would like your events to appear on the joint calendar, be sure to add them! Contact any of the organizers if you need permission to do so.
Yay for logic!
Shay Logan
Dear Cheerful Logicians and Friends of Logic,
Supergroup announcement time! Brief Summary: There are two talks to announce, one on Tuesday and one on Thursday. On Tuesday, María del Rosario Martínez Ordaz will talk to us about defective theories in the Seminario de Lógica Iberoamericana. On Thursday, Elisángela Ramírez will talk to us about connexive logic in the supergroup talk of the week. Details below.
Supergroup Talk:
Speaker: Elisángela Ramírez
Title: Relating Semantics for NL
Time and Date: Thursday, July 30, 8 pm GMT-5
Link: https://ksu.zoom.us/j/93077202104?pwd=VjJ4S0Z1QnRsd1B1SVQxbW9RbzJ2Zz0
Meeting ID: 930 7720 2104
Passcode: connexive
Abstract: This talk is based on the following claim: The connexive logic axiomatized in Nelson's Intensional Relations (NL) can be provided with a relational semantics in the style of the ones described by Jarmużek and Malinowski in their Boolean Connexive Logics.
I will offer an overview of both relational semantics for Boolean connexive logics, and the intensional vocabulary included in NL. Then I will go over the process behind obtaining a relational semantics for NL, with an emphasis on the proof for the only contraclassical axiom in the logic. Finally, I will compare the resulting semantics with two connexive logics considered by Jarmużek and Malinowski.
Talks by Member Groups:
Seminario de Lógica Iberoamericana:
Speaker: María del Rosario Martínez Ordaz
Title: Understanding defective theories: From logic to epistemology
Time and Date: Tuesday, July 28, 12:30pm (GMT-3)
Link: https://us02web.zoom.us/j/85024956727?pwd=RzBSRnUzQkluMUI3LzRtcUUrdXRIQT09
Meeting ID: 850 2495 6727
Password: 377551
Abstract: Here I aim at providing responses to two questions from the epistemology of logic, namely: can logicians achieve legitimate understanding of defective theories? and if so, how is this possible? On the one hand, understanding has been traditionally considered to "consist of knowledge about relations of dependence. When one understands something, one can make all kinds of correct inferences about it" (Ylikoski 2013: 100). In addition, understanding is often regarded as factive, this is, the content of understanding can only include true proposi tions that are known to be so. This considered, it is impossible to understand a knowingly defective (conicting, inconsistent, false and even impossible) set of information. On the other hand, much scientific practice in logic and other formal disciplines makes use of defective theories. And, despite the fact that some of these theories are knowingly defective, formal scientists have found different ways of scrutinizing and working with them to the point that they report having 'understood' both the theories as well as the phenomena that they describe. The formal apparatuses that they use to, allegedly, gain such an understanding are extremely varied and most of the time they go against some of the basic principles of classical logic. The combination of these facts poses the following dilemma: either understanding defective theories is possible or formal scientists that report having understood any defective theory are mistaken. Hence the importance of addressing both issues together.