https://www.gu.se/en/flov/the-lindstrom-lectures

We are proud to announce that the 2024 Lindström Lectures will be delivered by
**Phokion G. Kolaitis**, Distinguished Research Professor at UC Santa Cruz and a
Principal Research Staff Member at the IBM Almaden Research Center, US.
Professor Kolaitis will deliver a **public lecture on Monday, 15 April 2024,
1800–2000** and a **research lecture on Wednesday, 17 April at 10–12**. Both
lectures will be held in the Faculty of Humanities, University of Gothenburg.
The public lecture will also be broadcast over Zoom. A Zoom link for the event
will be distributed on the
Nordic Online Logic Seminar
mailing list.

**Monday, 15 April 2024 at 18:00 (UTC+2)** at the Faculty of Humanities,
University of Gothenburg and over Zoom

**Phokion G. Kolaitis** (University of California Santa Cruz and IBM Research)

*Characterizing Rule-based Languages*

Abstract: There is a mature body of work in logic aiming to characterize logical
formalisms in terms of their structural or model-theoretic properties. The
origins of this work can be traced to Alfred Tarski’s program to characterize
metamathematical notions in “purely mathematical terms” and to Per Lindström’s
abstract characterizations of first-order logic. For the past forty years,
rule-based logical languages have been widely used in databases and in related
areas of computer science to express integrity constraints and to specify
transformations in data management tasks, such as data exchange and
ontology-based data access. The aim of this talk is to present an overview of
more recent results that characterize various classes of rule-based logical
languages in terms of their structural or model-theoretic properties.

**Wednesday, 17 April 2024 at 10:00 (UTC+2)**

**Phokion G. Kolaitis** (University of California Santa Cruz and IBM Research)

*Homomorphism Counts: Expressive Power and Query Algorithms*

Abstract: A classical result by Lovász asserts that two graphs G and H are
isomorphic if and only if they have the same left profile, that is, for every
graph F, the number of homomorphisms from F to G coincides with the number of
homomorphisms from F to H. A similar result is also known to hold for right
profiles, that is, two graphs G and H are isomorphic if and only if for every
graph F, the number of homomorphisms from G to F coincides with the number of
homomorphisms from H to F. During the past several years, there has been a study
of equivalence relations that are relaxations of isomorphism obtained by
restricting the left profile or the right profile to suitably restricted classes
of graphs, instead of the class of all graphs. Furthermore, a notion of a query
algorithm based on homomorphism counts was recently introduced and investigated.
The aim of this talk is to present an overview of some of the main results in
this area with emphasis on the differences between left homomorphism counts and
right homomorphism counts.

The Nordic Online Logic Seminar
is organised monthly over Zoom, with expository talks on topics of interest for
the broader logic community. The seminar is open for professional or aspiring
logicians and logic aficionados worldwide. If you wish to receive the Zoom ID
and password for it, as well as further announcements, please subscribe here:

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**Date**: Monday, ~~26 February~~ 4 March 2024 at 16:00 CET (UTC+1) on Zoom

**Speaker:** Lauri Hella, Professor at the Faculty of Information Technology and
Communication Sciences, Tampere University

**Title:** Game characterizations for the number of quantifiers

**Abstract**

A game that characterizes definability of classes of structures by first-order
sentences containing a given number of quantifiers was introduced by Immerman
in 1981. In this talk I describe two other games that are equivalent with the
Immerman game in the sense that they characterize definability by a given number
of quantifiers.

In the Immerman game, Duplicator has a canonical optimal strategy, and hence Duplicator can be completely removed from the game by replacing her moves with default moves given by this optimal strategy. On the other hand, in the other two games there is no such optimal strategy for Duplicator. Thus, the Immerman game can be regarded as a one-player game, but the other two games are genuine two-player games.

The talk is based on joint work with Kerkko Luosto.

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**Date**: Monday, 29 January 2024 at 16:00 CET (UTC+1) on Zoom

**Speaker**: Peter Pagin, Professor Emeritus at the Department of Philosophy at
Stockholm University

**Title**: Switcher Semantics and quantification

**Abstract**:

Switcher Semantics is a semantic framework that is basically characterised by
allowing *switching*: when recursively applying a semantic function *μ* to a
complex term *t*, the semantic function applying to an immediate subterm *t’* of
*t* may be a function *μ’*, distinct from *μ*. An operator-argument-position
pair is called a *switcher* if it induces such a switch. Switcher semantic
systems do not satisfy the standard form of compositionality, but a generalized
form, which allows greater flexibility. In earlier work (mostly published), some
together with Kathrin Glüer, some with Dag Westerståhl, it has been applied to
natural language constructions like proper names in modal contexts, general
terms in modal contexts, indexicals in temporal contexts, quotation, and belief
contexts. This talk will focus on quantifiers and quantification. First-order
quantifiers can be regarded as switchers, switching from truth conditions to
satisfaction conditions. The larger topic is quantification into switched
contexts. I shall begin by giving an introduction to the framework.

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**Date**: Monday, 18 December 2023 at 16:00 CET (UTC+1) on Zoom

**Speaker:** Göran Sundholm (Professor of Logic (em.), Leiden University

**Title:** Curry-Howard—a meaning explanation or just another realizability interpretation?

**Abstract**

Around 1930 a major paradigm shift occurred in the foundations of mathematics;
we may call it the METAMATHEMATICAL TURN. Until then the task of a logician had
been to design and explain a full-scale formal language that was adequate for
the practice of mathematical analysis in such a way that the axioms and rules of
inference of the theory were rendered evident by the explanations.

The metamathematical turn changed the status of the formal languages: now they became (meta)mathematical objects of study. We no longer communicate with the aid of the formal systems – we communicate about them. Kleene’s realizability (JSL 1945) gave a metamathematical (re-)interpretation of arithmetic inside arithmetic. Heyting and Kolmogorov (1931-2), on the other hand, had used “proofs” of propositions, respectively “solutions” to problems, in order to explain the meaning of the mathematical language, rather than reinterpret it internally.

We now have the choice to view the Curry-Howard isomorphism, say, as a variant of realizability, when it will be an internal mathematical re-interpretation, or to adopt an atavistic, Frege-like, viewpoint and look at the language as being rendered meaningful. This perspective will be used to discuss another paradigm shift, namely that of distinguishing constructivism and intuitionism. The hesitant attitude of Gödel, Kreisel, and Michael Dummett, will be spelled out, and, at the hand of unpublished source material, a likely reason given.

]]>The Program Committee cordially invites all researchers, European and non-European, to submit their papers in all areas related to computability. Instructions for submission, both formal and informal, is available through the conference webpage https://events.illc.uva.nl/CiE/CiE2024/.

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**Date**: Monday, 27 November, 2023, during 15:00–16:30 CET (UTC+1) on
Zoom

**Speaker:** Sonja Smets, professor in Logic and Epistemology at the Institute
for Logic, Language and Computation, University of Amsterdam

**Title:** Reasoning about Epistemic Superiority and Data Exchange

**Abstract**

In this presentation I focus on a framework that generalizes dynamic epistemic
logic in order to model a wider range of scenarios including those in which
agents read or communicate (or somehow gain access to) all the information
stored at specific sources, or possessed by some other agents (including
information of a non-propositional nature, such as data, passwords, secrets
etc). The resulting framework allows one to reason about the state of affairs in
which one agent (or group of agents) has ‘epistemic superiority’ over another
agent (or group). I will present different examples of epistemic superiority and
I will draw a connection to the logic of functional dependence by A. Baltag and
J. van Benthem. At the level of group attitudes, I will further introduce the
new concept of ‘common distributed knowledge’, which combines features of both
common knowledge and distributed knowledge. This presentation is based on joint
work with A. Baltag in [1].

[1] 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, 73:90-110, 2020. https://doi.org/10.29007/plm4

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**Date**: Monday, 30 October 2023, at 16:00 CET (UTC+1) on Zoom

**Speaker:** Dag Westerståhl (Stockholm University, Tsinghua University)

**Title:** From consequence to meaning—the case of intuitionistic propositional logic (IPL)

**Abstract**

One quarter of the talk presents background on how facts about entailments and
non-entailments can single out the constants in a language, and in particular on
an idea originating with Carnap that the standard relation of logical
consequence in a formal language should fix the (model-theoretic) meaning of its
logical constants. Carnap’s focus was classical propositional logic (CPL), but
his question can be asked for any logical language. The rest of the talk gives a
very general positive answer to this question for IPL: the usual IPL consequence
relation does indeed determine the standard intuitionistic meaning of the
propositional connectives, according to most well-known semantics for IPL, such
as Kripke semantics, Beth semantics, Dragalin semantics, topological semantics,
and algebraic semantics.

The 2024 meeting will run for five days and comprise 10 plenary lectures, 3 tutorials and 6 special sessions as well as contributed talks. In addition, the 2024 Gödel Lecture will be delivered at the meeting.

The programme committee invites proposals for contributed talks. These can be on published or unpublished work, as well as work in progress. Instructions for submission will be made available through the conference webpage https://lc2024.se.

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**Date**: Monday, 25 September 2023 at 16:00 CEST (UTC+2) on Zoom

**Speaker:** Thomas Bolander (Professor in logic and AI at DTU Compute,
Technical University of Denmark)

**Title:** Epistemic Planning—Logical formalism, computational complexity, and robotic implementations

**Abstract**

Dynamic Epistemic Logic (DEL) can be used as a formalism for agents to represent
the mental states of other agents: their beliefs and knowledge, and potentially
even their plans and goals. Hence, the logic can be used as a formalism to give
agents, e.g. robots, a Theory of Mind, allowing them to take the perspective of
other agents. In my research, I have combined DEL with techniques from automated
planning in order to describe a theory of what I call Epistemic Planning:
planning where agents explicitly reason about the mental states of others. The
talk will introduce epistemic planning based on DEL, address issues of
computational complexity, and demonstrate applications in cognitive robotics and
human-robot collaboration.

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**Date**: Monday, 28 August 2023 at 16:00 CEST (UTC+2) on Zoom

**Speaker:** Thomas Ågotnes, Professor of Information Science, University of
Bergen (Norway) and Professor of Logic, Shanxi University (China)

**Title:** Somebody Knows and Weak Conjunctive Closure in Modal Logic

**Abstract**

Normal modal logics are closed under conjunctive closure. There are, however,
interesting non-normal logics that are not, but which nevertheless satisfy a
weak form of conjunctive closure. One example is a notion of group knowledge in
epistemic logic: somebody-knows. While something is general knowledge if it is
known by *everyone*, this notion holds if it is known by *someone*.
Somebody-knows is thus weaker than general knowledge but stronger than
distributed knowledge. We introduce a modality for somebody-knows in the style
of standard group knowledge modalities, and study its properties. Unlike most
other group knowledge modalities, somebody-knows is not a normal modality; in
particular it lacks the conjunctive closure property. We provide an equivalent
neighbourhood semantics for the language with a single somebody-knows modality,
together with a completeness result: the somebody-knows modalities are
completely characterised by the modal logic EMN extended with a particular weak
conjunctive closure axiom. The neighbourhood semantics and the completeness and
complexity results also carry over other logics with weak conjunctive closure,
including the logic of so-called local reasoning (Fagin et al., 1995) with
bounded “frames of mind”, correcting an existing completeness result in the
literature (Allen 2005). The talk is based on joint work with Yi N. Wang.