Welcome to my homepage!
I am an Emeritus of Logic and Theoretical Computer Science at the University of Bern. I received my mathematical education at the Ludwig-Maximilians-Universität in Munich. My principal research interests include proof theory (in particular the proof-theoretic analysis of subsystems of set theory and second order arithmetic), explicit mathematics and operational set theory, non-classical logics, philosophical foundations of mathematics (more specifically the relationship between predicative, metapredicative, and impredicative mathematics), as well as applications of logical methods in computer science.
Email: gerhard.jaeger@unibe.ch
Publications
Preprints and online first
G. Jäger, Explicit Weyl, to appear.
2025
G. Jäger, Gentzen in the 3- and 4-valued jungle, to appear.
2024
M. Bärtschi, G. Jäger, Some set-theoretic reduction principles, in: T. Piecha, K. Wehmeier (eds.), Peter Schroeder-Heister on Proof-Theoretic Semantics, Outstanding Contributions to Logic 29, Springer, 2024, 425-442, [pdf].
G. Jäger and M. Rathjen, Admissible extensions of subtheories of second order arithmetic, Annals of Pure and Applied Logic, 175,7 (2024), [pdf].
G. Jäger, Tame and full strict $\Pi^1_1$ reflection: A proof-theoretic approach, Journal of Logic and Computation, 34,6 (2024), 1082-1107.
2023
G. Jäger, Identity, Equality, and Extensionality in Explicit Mathematics, in: D. Bridges, H. Ishihara, M. Rathjen, H. Schwichtenberg (eds.), Handbook of Constructive Mathematics, Mathematics and Its Applications 185, Cambridge University Press, 2023, 564-583, [pdf].
2022
G. Jäger, Simplified cut elimination for Kripke-Platek set theory, in: F. Ferreira, R. Kahle, G. Sommaruga (eds), Axiomatic Thinking II, Springer; 2022, 9-34, [pdf].
G. Jäger, Stage comparison, fixed points, and least fixed points in Kripke-Platek environments, Notre Dame Journal of Formal Logic, 63,4 (2022), 443-461, [pdf].
2021
G. Jäger, Short note: Least fixed points versus least closed points, Archive for Mathematical Logic; 60 (2021), 831-835, [pdf].
2020
M. Bärtschi and G. Jäger, Having a look again at some theories of proof-theoretic strength around $\Gamma_0$, in: R. Kahle, M. Rathjen (eds.), The Legacy of Kurt Schütte, Springer, 2020, 103-128, [pdf].
2019
B. Afshari, G. Jäger, G.E. Leigh, An infinitary treatment of full mu-calculus, in: R. Iemhoff, M. Moortgat, R. de Queiroz (eds.), WoLLIC 2019, Lecture Notes in Computer Science, 11541, Springer, 2019, 17-34, [pdf] [bibiliographic data].
G. Jäger, S. Steila, From Mathesis Universalis to fixed points and related set-theoretic concepts, in: S. Centrone, S. Negri, D. Sarikaya, P.M. Schuster (eds.), Mathesis Universalis, Computability and Proof, Synthese Library, Studies in Epistemology, Logic, Methodology, and Philosophy of Science, Volume 412, Springer, 2019, 113-129, [pdf].
2018
G. Jäger, T. Rosebrock, K. Sato, Truncation and semi-decidability notions in applicative theories, The Journal of Symbolic Logic, 83,3 (2018), 967-990, [pdf],[bibliographic data].
G. Jäger, S. Steila, About some fixed point axioms and related principles in Kripke-Platek environments, The Journal of Symbolic Logic, 83,2 (2018), 642-668, [pdf], [bibiliographic data].
2017
G. Jäger, The operational penumbra: some ontological aspects, in: G. Jäger, W. Sieg (eds), Feferman on Foundations: Logic, Mathematics, Philosophy, Outstanding Contributions to Logic, 13, Springer, 2017, 253-283, [pdf].
2016
G. Jäger, Relativizing operational set theory, The Bulletin of Symbolic Logic, 22,3 (2016), 332-352, [pdf].
G. Jäger, M. Marti, Intuitionistic common knowledge and belief, Journal of Applied Logic, 18 (2016), 150-163, [pdf].
G. Jäger, M. Marti, A canonical model construction for intuitionistic distributed knowledge, in: L. Beklemishev, S. Demri, A. Mate (eds.), Advances in Modal Logic, 11, College Publications, 2016, 420-434, [pdf].
U. Buchholtz, G. Jäger, T. Strahm, Theories of proof-theoretic strength $\varpsi(\Gamma_{\Omega+1})$, in: D. Probst, P. Schuster (eds.), Concepts of Proof in Mathematics, Philosophy, and Computer Science, Ontos Mathematical Logic, vol. 6, De Gruyter, 2016, 115-140, [pdf].
2015
G. Jäger, D. Probst, A proof-theoretic analysis of theories for stratified inductive definitions, in: R Kahle, M. Rathjen (eds.), Gentzen's Centenary: The Quest for Consistency, Springer, 2015, 425-454, [pdf].