Journées sur les Arithmétiques Faibles
Weak Arithmetics Days 44

8-10 September 2025, Prague, Czech Republic

Aim. Weak arithmetics play a fundamental role in several areas of philosophy, mathematics, and computer science, by studying the nature and properties of natural numbers from a logical point of view. The aim of the conference is to provide a forum for researchers to present their results to members of communities who study or apply weak arithmetics in various fields and formalisms. Previous JAFs.

Topics. Proofs in arithmetic with restricted system of axioms; non-standard models of such systems; decidability, undecidability, and complexity of arithmetical theories; definability in arithmetic structures; machines, automata and words, related to arithmetic; finite model theory, word structures.

Location. Institute of Mathematics, Czech Academy of Sciences. The institute is in the centre of Prague, a few minutes walk from Wenceslas Square. The address is Žitná 25, 110 00 Praha 1.

Programme. Invited speakers:

• Albert Atserias, Technical University of Catalonia, TBA
• Emil Jeřábek, Czech Academy of Sciences, Mathematics in VTC₀
• Leszek Kołodziejczyk, University of Warsaw, Gauging the strength of (infinite) Ramsey's theorem for pairs: first-order consequences, the effect of the base theory, influence on proof size
• Jan Krajíček, Charles University, Extensions of models of bounded arithmetic

Contributed talks:

• Saeideh Bahrami, Lascar generic automorphisms of models of Peano arithmetic
• Julien Daoud, Speedups for Presburger Arithmetic and Real Closed Fields
• Azza Gaysin, Proof complexity of Mal’tsev CSPs
• Piotr Gruza, Tightness and semantic tightness in subtheories of Peano arithmetic
• Quentin Le Houerou, Ramsey-like theorems for separable permutations
• Ondřej Ježil, Prime Factorization in Models of PV₁
• Juvenal Murwanashyaka, Variants of adjunctive set theory which are not sequential
• Alexei Semenov, Definability lattices for very weak arithmetics
• Mengzhou Sun, On the finite cohesiveness principle
• Patryk Szlufik, Scott ranks of models of elementary arithmetic
• Yosuke Watanabe, A Formalization of Real Complexity Theory

Contributed talks. Authors are invited to send an abstract not exceeding three pages as an electronic submission in the form of a pdf file, to be sent both to cegielski@u-pec.fr and to thapen@math.cas.cz. Submissions are to be received before 7 July 2025.

Accommodation. There are many hotels within walking distance. Two very close nearby, which the institute sometimes uses for visitors, are EA Hotel New Town and Hotel Archibald City. We have not made any special arrangements with them for the meeting.

Registration. To register, send your details (full name, affiliation, planned dates of arrival and departure) to thapen@math.cas.cz. There is no conference fee. Please register if possible by 17 August so we have an idea of numbers.

Contact. For any enquires contact Patrick Cégielski, cegielski@u-pec.fr or Neil Thapen, thapen@math.cas.cz.

JAF steering committee. Patrick Cégielski (Paris XII), Julien Cervelle (Paris XII), Andrés Córdon-Franco (Seville), Ali Enayat (Göteborg), Costas Dimitracopoulos (Athens), Alex Esbelin (Clermont-Ferrand), Neil Thapen (CAS)

Local organizing committee. Neil Thapen (CAS), Pavel Hrubeš (CAS), Ondřej Ježil (Charles University)

Sponsors / organizers.

Header image of the astronomical clock in Old Town Square by Txllxt TxllxT, CC BY-SA 4.0