Initiated by the center’s students and researchers in 2019, the Tsinghua Logic Salon has quickly grown into a lively platform for try-outs and exchanges of new ideas. Researchers in various fields of logic are invited to present their latest research, as well as the challenges that they see. Every participant is encouraged to engage in discussions and exchange of perspectives. Each session lasts for 1.5 hours in total, with 30 minutes of discussion included.
Organizing Committee (since September 2023): Junhua Yu, Chenwei Shi, Wei Wang, Jialiang Yan, Penghao Du.
■ Schedule for 2024-2025 academic year (Spring)
| Date | Speaker |
|---|---|
| 2025 Feb 20 | Kazuyuki Tanaka |
| 2025 Feb 27 | Benedikt Loewe |
| 2025 Mar 20 | Youan Su |
| 2025 Mar 27 | Jieting Luo |
| 2025 Apr 10 | Han Xiao, Tomasz Jarmużek |
| 2025 Apr 24 | Huaqing Cheng |
| 2025 May 08 | Wei Zhu |
| 2025 May 22 | Eleonora Cresto |
| 2025 May 29 | Daniyar Shamkanov |
■ Current Events
2025 Jun 12 16:00-17:30 Carlo Cordasco (University of Manchester) The Accuracy-Explainability trade-off and its implication
Vredenburgh (2021) argues for a collective interest in “explainability” of machine‐learning outputs on the grounds that, without genuine causal explanations, agents lack the means to revise their strategies. This paper begins by examining the implicit theory of explanation at stake, showing it must satisfy two classical desiderata: truth‐tracking (each explanans must be factually and causally sound) and verifiability (the inferential steps must be inspectable and checkable). I then introduce a decision‐theoretic model—analogous in human hiring and grading—demonstrating that imposing fully transparent, ex-ante rules enforces a shallow proof structure but forfeits accuracy when novel, unanticipated data arise. By contrast, any rule that learns and adapts must embed latent premises, deepening the “proof tree” and eluding ex-ante inspection. This accuracy–explainability trade-off undermines Vredenburgh’s case for an unqualified Right to Explanation in dynamic contexts, for it shows that insisting on deductive transparency can incur unacceptable epistemic and practical costs.
2025 Jun 05 16:00-17:30 Graham Priest (Graduate Center, City University of New York) Überconsistent Logics and Dialetheism
For many decades now, logics which permit inconsistent but non-trivial theories have been investigated and discussed. However, of recent years, we have seen the recognition that there are logics which not only permit contradictions, but which deliver contradictions: the logical truths are themselves inconsistent. As yet, they have no standard name as far as I know. Let us call them überconsistent logics. Dialetheism is the view that some contradictions are true. It might well be thought that these logics which deliver contradictory logical truths provide a slam dunk for dialetheism. After all, as Quine puts it, ‘if sheer logic is not conclusive, what is?’ Matters are not that straightforward, however. This talk is an initial investigation of the relationship between überconsistent logics and dialetheism. In the first part of the talk I give the appropriate background for the discussion. In the second I discuss how three well known überconsistent logics bear on the matter of dialetheism.
2025 May 24 10:00-11:30 Eleonora Cresto (Universidad de San Andrés, CONICET/IIF-SADAF) Dynamic Logic for Ungrounded Payoffs
Higher order likes and desires sometimes lead agents to have ungrounded or paradoxical preferences. This situation is particularly problematic in the context of games. If payoffs are interdependent, the overall assessment of particular courses of action becomes ungrounded; in such cases the matrix of the game is radically under-determined. Paradigmatic examples of this phenomenon occur when players are ‘perfect altruists’ or ‘perfect haters’, in a sense to be explained. In this paper I rely on a dynamic doxastic logic to mimic the search for a suitable matrix. Upgrades are triggered by conjectures on other players’ utilities, which can in turn be based on behavioral or verbal cues. We can prove that, under certain conditions, pairs of agents with paradoxical preferences eventually come to believe that they are not able to interact in a game. As a result I hope to provide a better understanding of game-theoretic ungroundedness, and, more generally, of the nuances of higher order preferences and desires.
2025 May 08 14:00-15:30 Wei Zhu (朱薇, University of Padua) Consistency Violation Counting Algorithm: A Belief-First Approach to Ranking Functions
Spohn’s ranking function provides a semi-quantitative, quasi-probabilistic measure for an algebra A over a set of possibilities W, assigning numerical values to sets in A and thus raising a question of how to interpret and generate non-trivial ranking numbers. In this paper, we adopt a belief-first epistemological perspective and introduce a new consistency violation counting algorithm(CVCA), which generates ranking numbers based on an agent’s existing beliefs. The central idea of CVCA is to assign a unique numerical value to a proposition by counting the minimal number of reference beliefs it contradicts. To develop this approach, we first introduce two assumptions regarding a reference set and how the CVCA works. Based on these assumptions, we define CVCA and demonstrate its constructive feature by proposing two implementation methods: one using kernel contraction in belief revision theories and the other the breadth-first search algorithm in computer science. Finally, we show how ranking numbers can be generated and explained by integrating a belief-first epistemological view, a computational algorithm, and a ranking function into a unified framework.
2025 Apr 24 16:00-17:30 Huaqing Cheng (程华清, Anhui Normal University) The S5 Modal Expansion of Intuitionistic First-Order Logic with a Layered Intuitive Interpretation
There exist various works on intuitionistic modal logics which originate from different sources. In this talk, I will construct the system ILS5 (the S5 modal expansion of intuitionistic first-order logic) which maintains the Brouwer-Heyting-Kolmogorov (BHK) interpretation. Meanwhile, I will explore whether ILS5 accepts the Barcan Formula from two perspectives: intuitive interpretation and relational semantics.In providing an intuitive interpretation for ILS5 based on the BHK interpretation, the main difficulty is that the BHK interpretation is confined to first-order logical constants, because logic relies on mathematics in intuitionism. So I will provide a layered intuitive interpretation for ILS5. In this interpretation, the Barcan formula will not be accepted as a general principle within ILS5. This interpretation relies on a hierarchy of truths between intuitionistically necessary truth and classically necessary truth. The proto-ontological difference between Brouwer’s mathematical intuitionism and classical mathematics (C. Posy proposes) can provide the philosophical foundation for this hierarchy.I will also construct a relational semantics for ILS5 based on a slight variation of a frame which K. Došen gives. This semantics can help to show that the Barcan formulais not a theorem of ILS5. Basic properties of the ILS5 model will be shown. Typical metatheorems of ILS5 e.g. the monotonicity theorem, soundness theorem, and completeness theorem will be proved. Finally, this semantics has an interesting application in modeling knowledge and belief transfer in social settings.
2025 Apr 10 16:00-17:30 Tomasz Jarmużek (杨木泽, Nicolaus Copernicus University) Introduction to relating semantics with selected application examples
Relating logic is a logic of relating connectives — just as Modal Logic is a logic of modal operators. The basic idea behind relating connectives is that the logical value of a given complex proposition is the result of two things:
(i) the logical values of the main components of this complex proposition; supplemented with
(ii) a valuation of the relation between these components.
The latter element is a formal representation of an intensional relation that emerges from the connection of several simpler propositions into one more complex proposition. In the presentation I will present a general outline of relating semantics and selected application examples (introductory article: Relating Semantics as Fine-Grained Semantics for Intensional Logics, https://link.springer.com/chapter/10.1007/978-3-030-53487-5_2).
2025 Apr 10 14:00-15:30 Han Xiao (肖汉, University of Hamburg) Impossibility of finite axiomatisation of generalized Medvedev and spiked Boolean logics
In this talk, I will present the proof of Nick Bezhanishvili’s conjectures on generalized Medvedev logics, which is a joint work with Gaëlle Fontaine, and provide an overview of the landscape of this class of logics. Additionally, I will discuss a strengthened version of Inamdar’s conjecture on the logic of spiked Boolean algebras. If time permits, I will also share some very very recent ideas on a potential result related to Cheq logic.
2025 Mar 27 16:00-17:30 Jieting Luo (罗捷婷 Zhejiang University) Learning from Small Data for Personalization: Logic-based Approaches
Large Language Models (LLMs) have demonstrated remarkable capabilities in natural language processing. Fine-tuning these models involves adapting a pre-trained model to specific tasks or domains using smaller datasets, thereby enhancing their performance and relevance. While machine learning techniques are commonly employed for fine-tuning, logic-based approaches—inspired by neural-symbolic learning and formal learning theory—offer an alternative pathway. In this talk, I will present two projects that utilize logic-based methods to enable autonomous agents to learn effectively from limited data, facilitating personalized outcomes. The first project focuses on tailoring explanations through conversational interactions, while the second aims to infer desires from emotions. Both projects highlight the potential of logic-based fine-tuning in enabling agents to achieve sophisticated understanding and reasoning with small data.
2025 Mar 20 16:00-17:30 Youan Su (苏有安 Liaoning University) Craig’s Interpolation in Intuitionistic Epistemic Logic IEL with Distributed Knowledge
This talk will focus on the Craig interpolation theorem, including its meaning, history, and applications. We will present a standard proof-theoretic approach known as Mahara’s method to demonstrate the proof of this theorem. The foundational system under consideration is a first-order intuitionistic epistemic logic IEL with distributed knowledge. We will demonstrate the Craig interpolation theorem in the system that does not include function symbols. The contents discussed are based on a collaborative work with Katsuhiko Sano and Ryo Murai.
2025 Feb 27 18:00-19:30 Benedikt Löwe (University of Hamburg and University of Cambridge) Modal logics of model constructions
This is a survey talk about modal logics of model constructions with a particular emphasis on modal logics of forcing. We shall discuss what we can learn from them, how we determine such a modal logic, and what the most relevant open questions are.
About the speaker: Professor Benedikt Löwe is a mathematician, logician, and philosopher based at the Universities of Hamburg and Cambridge. For decades he has been working in mathematical logic (especially set theory) and philosophy of mathematics. His personal webpage is https://www.math.uni-hamburg.de/home/loewe/index.html
2025 Feb 20 Kazuyuki Tanaka (Beijing Institute of Mathematical Sciences and Applications, 北京雁栖湖应用数学研究院) On collapsing phenomena of the alternation hierarchy of modal μ-calculus
Modal μ-calculus, introduced by D. Kozen, is a propositional modal logic extended with greatest and least fixpoint operators. In general, the μ-calculus is much more expressive than modal logic. The alternation hierarchy of μ-formulas is generated by calibrating the entanglement of the fixed-point operators in a μ-formula.
Alberucci and Facchini [1] demonstrated that the alternation hierarchy of the modal μ-calculus collapses to the alternation-free fragment over transitive frames (for K4) and further to modal logic over equivalence relations (for S5). We extend their results to a broader range of frames, and then characterize such collapsing phenomena in terms of special μ-equations.
Furthermore, we apply our findings to epistemic logics, investigating how the alternation hierarchy behaves in systems such as S4.2, S4.3, S4.3.2, and S4.4. From this perspective, we analyze degrees of ignorance in these logics, providing insights into their epistemic structures.
This research is conducted in collaboration with Dr. Leonard Pacheco (Institute of Science, Tokyo), and an earlier version of this work was presented in [2].
[1] L. Alberucci and A. Facchini. The modal μ-calculus hierarchy over restricted classes of transition systems. J. Symbolic Logic 74 (4) 1367 – 1400, 2009.
[2] L. Pacheco and K. Tanaka. The Alternation Hierarchy of the μ-calculus over Weakly Transitive Frames. WoLLIC 2022, LNCS 13468, 207-220, 2022.
田中一之教授博士毕业于美国加州大学伯克利分校，曾就职于东京工业大学和东北大学，并指导15位博士生和50名硕士生，2022年正式入职BIMSA。他是数理逻辑和计算理论领域的国际知名学者，在反推数学和二阶算术领域开创了新的研究方法，如WKLo的田中嵌入定理和守恒结果的田中公式，取得了一系列奠基性的成果，并将这一研究方向引入日本，将日本的数理逻辑研究推向了世界水平。田中一之教授还致力于模态mu演算，认知逻辑，随机博弈树等交叉领域的研究。
■Past Events
Click HERE to check the past events.
