The Delta Logic Workshops aim to bring logicians from Mathematics, Philosophy, and Computer Science together. The Delta 28 Logic Workshop will be held at Sun Yat-sen University, Zhuhai Campus.
Venue: A542, Haiqin 6, Department of Philosophy (Zhuhai), Sun Yat-sen University, No. 2 Daxue Road, Zhuhai
Time: Saturday, November 7, 2026
Invited speakers
Xiaozhou Che (Fudan University)
Haorui Chen (South China Normal University)
Yunsong Wang (Peking University)
Bokai Yao (Peking University)
Fengju Zhang (Sun Yat-sen University)
Teng Zhang (Zhejiang University of Science and Technology)
Programme
Morning Session (Chair: Jinhe Ye)
09:00–09:50 Xiaozhou Che: On weakly generic types in real formal series fields
Abstract: Weakly generic types are a fundamental notion for definable groups in NIP structures, capturing canonical translation-invariant generic behavior. In this talk, we study weakly generic types of 𝔾ₐⁿ and 𝔾ₘⁿ in a monster model 𝕄 of Th(ℝ((t))) or Th(ℝ((t^ℚ))) with value group Γ_𝕄. For 𝔾ₘⁿ, a type is weakly generic if and only if its valuation pushforward is weakly generic in Γ_𝕄ⁿ, and all such types are ∅-definable. For 𝔾ₐⁿ, we give a valuation-theoretic characterization in terms of polynomials and their partial derivatives. Most notably, in contrast to the multiplicative case, we prove that there exist undefinable weakly generic types in 𝔾ₐⁿ. We close with two open questions on the fine structure and classification of weakly generic types in the additive setting. This is joint work with Ningyuan Yao.
09:50–10:40 Haorui Chen: An improvement on the lifting of posets
Abstract: In this talk, we present an improvement on the lifting of partial order structures studied in previous work. This improvement provides a new method for constructing structures, allowing certain functions in the original structure as well as morphisms between structures to be lifted simultaneously. In particular, we apply this method to distributive lattices, obtaining a fundamental theorem for comparing classes of weak filters definable by quantifier-free positive formulas, which reduces the comparison of class-level inclusion relations to comparisons between finite structures. In addition, we attempt to demonstrate applications of this lifting method in other branches of mathematics.
10:40–11:10 Tea Break and Group Photo
11:10–12:00 Yunsong Wang: Problem semantics for intuitionistic logic
Abstract: The Brouwer–Heyting–Kolmogorov (BHK) interpretation understands formulas as problems and proofs as their solutions, offering a direct intuition for formulas and logical principles. Medvedev's problem semantics offers a concrete mathematical framework for this interpretation. However, the logic it yields, known as Medvedev logic, is a proper extension of intuitionistic propositional logic (IPC). The decidability of Medvedev logic remained a difficult open problem for decades. In September 2026, two works, both using generative AI, established its undecidability. Against this background, we revisit Medvedev's original aim of capturing intuitionistic logic itself through a precise semantics of problems and solutions. At the propositional level, we obtain two sound and complete problem semantics for IPC, inspired respectively by Friedman and Läuchli, thereby fulfilling Medvedev's original aim. Läuchli also explored a direct first-order extension, but it did not yield intuitionistic first-order logic (IQC). We identify the resulting logic and develop a more natural extension that captures IQC, proving soundness and completeness for both. In both the propositional and first-order settings, we establish a connection with constructive type theory, a central advantage of problem semantics. Building on these results, we plan to study intuitionistic mathematical theories and their constructive content through problem semantics.
12:00–14:30 Lunch Break
Afternoon Session (Chair: Liuzhen Wu)
14:30–15:20 Bokai Yao: The iterative conception reconsidered
Abstract: According to the iterative conception of set, sets are formed in stages. This familiar picture is often taken to justify many standard axioms of set theory. But what exactly does the iterative conception say? I investigate the conception in its most general form, isolating its minimal commitments.I argue that the basic iterative conception is not robust: its natural formalizations are not equivalent, and their models can have very different structures. I then consider further principles of stage-unboundedness and reflection. These principles restore robustness, but in doing so give rise to distinct conceptions of set.
15:20–16:10 Fengju Zhang: Identity crisis on tightly C⁽²⁾ compact cardinal
Abstract: Bagaria and Goldberg asked if κ being tightly C⁽ⁿ⁾-compact implies κ∈C⁽ⁿ⁺¹⁾ for natural numbers n≥1? Usuba gave a negative answer for n＝1. In this talk we give a negative answer for n＝2.
16:10–16:30 Tea Break
16:30–17:20 Teng Zhang: Super thick sets and their applications
Abstract: There are many combinatorial notions in arithmetic Ramsey theory, which usually contain rich combinatorial and algebraic structures. In this talk, we introduce a notion called super thick sets, we will show that it has some good properties, and we will provide several applications.
17:20–20:00 Dinner
Sponsors
National Natural Science Foundation of China
Department of Philosophy (Zhuhai), Sun Yat-sen University