Georg Lehner

I am a Postdoc in mathematics at Freie Universität Berlin, working as part of the research group "Algebraic Topology". My current area of focus is algebraic K-theory of group rings and the Farrell-Jones conjecture. In a broader sense my interests are everything related to group and representation theory, homotopy theory, higher category theory, differential topology, topos theory and matters related to categorical logic.

Norm and assembly for additive invariants of finite groups joint with Alex Müller and Holger Reich (in preparation)
Computing the negative K-theory of finite groups of order ≤100 (Preprint, submitted for publication 2024)
Group completion via the action ∞-category (Preprint, submitted for publication 2024)
The passage from the integral to the rational group ring in algebraic K-theory (Preprint, submitted for publication 2023)
PhD thesis under supervision of Prof. Holger Reich, Freie Universität Berlin. My thesis is centered around the question of understanding the map from the integral to the rational group ring in algebraic K-theory. Graduated November 22, 2021, Summa Cum Laude.
Masters thesis under supervision of Prof. Holger Reich and Prof. Gavril Farkas, Humboldt Universität zu Berlin, 2018

"Norm, assembly and coassembly" 28.10.2025 @Universität Münster, Oberseminar Topology, Notes

"Norm, assembly and coassembly" 10.9.2024 @"Dualizable Categories & Continuous K-Theory", MPIM, Bonn. Slides

"Norm, assembly and coassembly" 14.5.2024 @"From Analysis to Homotopy Theory", Greifswald. Slides

"Rigidity and the Rosenberg Conjecture" 27.4.2024 @33rd NRW Topology Meeting, University of Wuppertal

"Group Completion via the action ∞-category" 15.4.2024 @(∞,n)-Categories and their applications, Utrecht University

"Group completion of E_n - Spaces and infinite products" 8.2.2024, @University Regensburg

Research stay, 4-6.12.2023 @University Copenhagen

"The Rosenberg Conjecture through the lens of solidification" 21.7.2023, @Potsdam University Notes

"The map K_0 ZG -> K_0 QG" 2021, @GROOT Summer Seminar 2021

"What is the point of pointless topology?" 2019, @Berlin Mathematical School's "What is...?" Seminar

"What is a topological surface?" 2018, @Berlin Mathematical School's "What is...?" Seminar

Winter Semester 2024/25

Analysis 3, with Holger Reich
Topology and Topoi, lecture series.
You can find handwritten lecture notes and exercise sheets by clicking the links.
Online-Seminar on C*-Algebras and their K-theory, joint with Anupam Datta (Bonn) and Devarshi Mukherjee (Münster). (If you are interested, ask me via email for a Zoom-link and/or notes.)