At conferences/summer schools etc.:

2026

• The Spherical Hopf Algebra at Groups and Geometry in North-Rhine Westphalia, April 30, Universität Münster, Münster, Germany
• The Motivic Alexander Module at Mini-Topology-Workshop, March 16, Universität Osnabrück, Osnabrück, Germany

2025

• Higher Spherical Scissors Congruence (joint talk with Josefien Kuijper and David Mehrle) at Scissors Congruence and K-theory, July 14, University of Pennsylvania, Philadelphia, Pennsylvania, USA
• Algebraic Knots from a Motivic point of view at Séminaire Algèbre et géométries, March 10, Institut Fourier, Grenoble, France

2024

• From Operations on Milnor-Witt K-theory to Motivic Knot Invariants at 34th NRW topology meeting, November 22, Universität Bielefeld, Bielefeld, Germany
• Higher Spherical Scissors Congruence (joint talk with Josefien Kuijper and David Mehrle) at Collaborative Workshop in K-theory and Scissors Congruence, August 02, VU, Nashville, Tennessee, USA
• From Operations on Milnor-Witt K-theory to Motivic Knot Invariants at PCMI 2024 Research Program: Motivic Homotopy Theory, July 26, PCMI, Park City, Utah, USA
• From Operations on Milnor-Witt K-theory to Motivic Knot Invariants at Oberseminar Topologie, June 19, Universität Münster, Münster, Germany

2023

• Operations between certain Motivic Stable Homotopy Sheaves of Spheres at Young Topologists Meeting 2023, July 25, EPFL, Lausanne, Switzerland
• Operations between various Homotopy Modules at Homotopy theory, K-theory and trace methods, July 06, Radboud University Nijmegen, Nijmegen, Netherlands
• Motivic Cohomology and Motives (teXed version here: Motivic Cohomology and Motives teXed) at Talbot 2023: Computations in motivic stable homotopy theory, June 05, The Shire in the woods, McGrath, Minnesota, USA
• Operations on Milnor-Witt K-theory at Oberseminar Algebra und Topologie, January 11, BUW, Wuppertal, Germany

2022

• Motivic Poincaré Series and Stratifications at Grothendieck ring and Derived category: a gathering, April 27, Università di Torino, Turin, Italy

2021

• Motivic point counting at London Junior Number Theory Seminar, June 01, Imperial College London, Online

2020

• Making the p-adic's motivic at 2020 Summer Tropical Algebraic Geometry Online SeminAUR (STAGOSAUR): Top Weight Cohomology of Moduli Spaces of Curves, July 21, Online
• Moduli space of stable curves at 2020 Summer Tropical Algebraic Geometry Online SeminAUR (STAGOSAUR): Top Weight Cohomology of Moduli Spaces of Curves, July 03, Online

At local seminars etc.:

2026

• Applications to Oriented Grassmannians at Oberseminar Topologie (on Chow-Witt-Rings with Applications to the Geometry of Grassmannians), June 10, Universität Osnabrück
• An Invariant of Algebraic Knots at Oberseminar Algebra, April 15, Universität Osnabrück

2025

• The Homogeneous Spectrum of Milnor-Witt K-theory of a Field at Oberseminar Topology (on Chromatic Motivic Homotopy Theory: Balmer Spectra of Motivic Categories), November 24, Universität Osnabrück
• Stable Results at Oberseminar Topology (on Motivic and Real Étale Homotopy Theory), July 02, Universität Osnabrück
• Stable Power Operations of Ordinary Mod p Cohomology at Oberseminar Topology (on The Motivic Sphere in Non-A^1-invariant Motivic Homotopy Theory and Stable Power Operations), February 26, Universität Osnabrück
• Cohomology Operations at Oberseminar Topology (on The Motivic Sphere in Non-A^1-invariant Motivic Homotopy Theory and Stable Power Operations), January 29, Universität Osnabrück

2024

• Affine Algebraic Groups are Linear at Oberseminar Algebraic Geometry (on Algebraic Groups), April 29, HHU Düsseldorf

2023

• Algebraic Stacks at Oberseminar Algebraic Geometry (on the Irreducibility of the space of curves), December 11, HHU Düsseldorf
• Knot (and Diagram) Quandles at Oberseminar on Algebra and Geometry (on Knots and Quandles), June 23, HHU Düsseldorf
• Operations on Milnor-Witt K-theory at Advanced Seminar on Group Theory (Research talks), May 02, HHU Düsseldorf
• Chern Classes und K_num at Oberseminar Algebraic Geometry (on Bridgeland Stability Conditions), April 17, HHU Düsseldorf

2022

• Néron-Severi Group and Mordell-Weil Lattice at Oberseminar Algebraic Geometry (on Elliptic Surfaces), December 05, HHU Düsseldorf
• (Operations on) Milnor-Witt K-theory at Oberseminar Model Theory (Research talks), November 22, HHU Düsseldorf
• Motivic Integration at Oberseminar Algebraic Geometry (on Motivic Integration), June 20, HHU Düsseldorf
• Classifying Topoi I at Oberseminar Model Theory (on Topos Theory), June 01, HHU Düsseldorf

2021

• Systems of Topologies at Oberseminar Model Theory (on the Étale-open Topology and Stable Large Fields), November 16, HHU Düsseldorf
• Derived Category and Canonical Bundle I: The Reconstruction Theorem of Bondal and Orlov at Oberseminar Algebraic Geometry (on Derived Categories of Coherent Sheaves), November 15, HHU Düsseldorf
• The What, Why and Where of a poor human's Motive (aka playing with scissors in Algebraic Geometry) at Non-professor meetings of the GRK2240 Workshop, November 11, HHU Düsseldorf

2020

• Triangulated Categories and Localization at GRK2240 Workshop (on Tensor-Triangular Geometry), May 05, Online

2019

• Motivic Integration and the Motivic Monodromy Conjecture at Non-professor meetings of the GRK2240 Workshop, December 05, BUW Wuppertal

Notes from my talks can be found under talks. Other (mostly rather old) notes:

Simplicial complexes and simplicial homology

A quick introduction to simplicial complexes (both geometric and abstract) up to the definition of simplicial homology. No prior knowledge is assumed.

Talbot 2023 talk 15: Vanishing results for the η-inverted Sphere

This is Viktor's talk from Talbot 2023: Computations in motivic stable homotopy theory, which I teXed and complemented. It is rather deep into the computation of the first motivic stable stem of the sphere and thus requires quite some prerequisites from stable motivic homotopy theory. The main result presented here is that the first and second motivic stable stems of the η-inverted sphere vanish.

The Witt group of the rational numbers

This note from a talk I once gave in a student seminar explains the computation of the Witt group of quadratic forms over the rational numbers by Milnor and Tate (as for example also found in Lam's book "Introduction to quadratic forms over fields"). The basic theory of quadratic forms and Witt groups/rings is assumed. Further-more assumes that the reader is comfortable enough with discrete valuations and surrounding objects like uniformizers, residue fields etc.

Where to find Milnor-Witt K-theory

Is a very short note explaining why you (the reader) might be interested in Milnor-Witt K-theory. No prior knowledge is assumed. Just lists various appearances with short background stories without even defining what Milnor-Witt K-theory is. Does hence not get into any technicalities.

At Universität Osnabrück:

Summer 27:

• -Lecturer for the course on Number Theory

Winter 26/27 (current):

• -Lecturer for the course on Field and Galois Theory

Summer 26:

• -Assistant (1 class) for the course on Linear Algebra II of Prof. Dr. Markus Spitzweck
• -Instructor for a student seminar on Category Theory
• -Organizer of the Oberseminar Topologie on Chow-Witt-Rings with Applications to the Geometry of Grassmannians

Winter 25/26:

• -Assistant (2 classes) for the course on Linear Algebra I of Prof. Dr. Markus Spitzweck
• -Organizer of the Oberseminar Topologie on Chromatic Motivic Homotopy Theory: Balmer Spectra of Motivic Categories

Summer 25:

• -Assistant (1 class) for the course on Analysis II of Prof. Dr. Oliver Röndigs
• -Organizer of the Oberseminar Topologie on Motivic and Real Étale Homotopy Theory

Winter 24/25:

• -Assistant (2 classes) for the course on Analysis I of Prof. Dr. Oliver Röndigs
• -Coorganizer of the Oberseminar Topologie on The Motivic Sphere in Non-A^1-invariant Motivic Homotopy Theory and Stable Power Operations

At HHU Düsseldorf:

Summer 24:

• -Assistant (2 classes) for the course on Linear Algebra I of Priv.-Doz. Dr. Karin Halupczok

Winter 23/24:

• -Assistant (2 classes) for the course on Mathematics for Computer Science I of Dr. Nadja Valentin

Summer 23:

• -Assistant (1 class) for the course on (Algebraic) Topology II of Jun.-Prof. Dr. Holger Kammeyer
• -Assistant (1 class) for the course on Linear Algebra I of Prof. Dr. Immanuel Halupczok
• -Coorganizer of the Oberseminar Algebra und Geometrie on Knot Theory and Quandles

Winter 22/23:

• -Assistant (1 class) for the course on (Algebraic) Topology I of Jun.-Prof. Dr. Holger Kammeyer
• -Assistant (1 class) for the course on Number Theory I (Algebraic Number Theory) of Priv.-Doz. Dr. Karin Halupczok

Summer 22:

• -Assistant (2 classes) for the course on (Abstract) Algebra of Prof. Dr. Immanuel Halupczok

Winter 21/22:

• -Assistant (1 class) for the course on Introduction to (Algebraic) Topology of Jun.-Prof. Dr. Holger Kammeyer
• -Assistant (1 class) for the course on Linear Algebra I of Prof. Dr. Marcus Zibrowius

Summer 21:

• -Assistant (2 classes) for the course on Linear Algebra II of Prof. Dr. Immanuel Halupczok

Winter 20/21:

• -Assistant (2 classes) for the course on Linear Algebra I of Prof. Dr. Immanuel Halupczok

Summer 20:

• -Assistant (2 classes) for the course on Linear Algebra I of Dr. Peter Arndt

Winter 19/20:

• -Assistant (1 class) for the course on (Algebraic) Topology I of Prof. Dr. Marcus Zibrowius

Summer 19:

• -Teaching assistant (1 class) for the course on Linear Algebra I of Dr. Sasa Novakovic
• -Instructor of revision classes of the course on Analysis I of Prof. Dr. Axel Grünrock

Winter 18/19:

• -Instructor of revision classes of the course on Analysis I of Prof. Dr. Oleg Bogopolski

Summer 18:

• -Instructor of revision classes of the course on (Abstract) Algebra of Prof. Dr. Immanuel Halupczok
• -Voluntary Instructor of support classes (1 class) of the course on (Abstract) Algebra of Prof. Dr. Immanuel Halupczok

Summer 17:

• -Instructor of revision classes of the course on Analysis I of Prof. Dr. Oleg Bogopolski

Winter 16/17:

• -Instructor of revision classes or the course on Linear Algebra I of Prof. Dr. Immanuel Halupczok
• -Voluntary Instructor of support classes (1 class) of the course on Linear Algebra I of Prof. Dr. Immanuel Halupczok

2027

• Scissors Congruence K-theory and Manifolds, May 30-June 04, Banff International Research Station, Banff, Canada

2026

• 38th NRW topology meeting, November 05-06, RUB, Bochum, Germany
• 37th NRW topology meeting, June 11-12, Universität Münster, Münster, Germany
• Groups and Geometry in North-Rhine Westphalia, April 30, Universität Münster, Münster, Germany
• Co-organizer of Workshop on Recent Advances in Motivic Cohomology: The Motivic Filtration for Algebraic K-theory, March 18-20, Universität Osnabrück, Osnabrück, Germany
• Mini-Topology-Workshop, March 16-17, Universität Osnabrück, Osnabrück, Germany

2025

• 36th NRW topology meeting, November 06-07, Mathematikzentrum der Universität Bonn, Bonn, Germany
• Motives and Arithmetic Geometry, July 28-August 01, TU Darmstadt, Darmstadt, Germany
• Scissors Congruence and K-theory, July 14-17, University of Pennsylvania, Philadelphia, Pennsylvania, USA
• Polylogarithms, homology of linear groups, and Steinberg modules, June 08-13, SwissMAP Research Station (SRS), Les Diablerets, Switzerland
• 35th NRW topology meeting, May 23-24, Universität Osnabrück, Osnabrück, Germany
• Workshop: Lurie's Elliptic Cohomology, March 31-April 04, BUW, Wuppertal, Germany

2024

• 34th NRW topology meeting, November 22-23, Universität Bielefeld, Bielefeld, Germany
• Collaborative Workshop in K-theory and Scissors Congruence, July 29-August 02, VU, Nashville, Tennessee, USA
• PCMI 2024 Research Program: Motivic Homotopy Theory, July 13-27, PCMI, Park City, Utah, USA
• Scissors congruences, algebraic K-theory and Steinberg modules, July 08-12, AIM, Pasadena, California, USA
• 33rd NRW Topology Meeting, April 26-27, BUW, Wuppertal, Germany
• Winter school on unstable motivic homotopy theory, March 11-15, JGU, Mainz, Germany

2023

• Algebraic K-theory and Redshift Fall school, September 18-22, JGU, Mainz, Germany
• Young Topologists Meeting 2023, July 24-28, EPFL, Lausanne, Switzerland
• Homotopy theory, K-theory and trace methods, July 05-07, Radboud University Nijmegen, Nijmegen, Netherlands
• Motivic and non-commutative aspects of enumerative geometry, July 03-05, Radboud University Nijmegen, Nijmegen, Netherlands
• Summer School on Scissors Congruence, Algebraic K-theory, and Trace Methods, June 26-30, IU, Bloomington, Indiana, USA
• Talbot 2023: Computations in motivic stable homotopy theory, June 04-10, The Shire in the woods, McGrath, Minnesota, USA

2022

• Co-organizer of Summer School on Motivic Integration, September 12-16, HHU, Düsseldorf, Germany
• Harnessing motivic invariants, June 27-July 01, UDE, Essen, Germany
• ICM 2022 Satellite "Motives and Related Topics", June 27-July 01, St. Petersburg, Russia
  replaced by "Harnessing motivic invariants"
• Algebraic K-theory, motivic cohomology and motivic homotopy theory, June 13-17, Isaac Newton Institute for Mathematical Sciences, Cambridge, UK
• Grothendieck ring and Derived category: a gathering, April 27-28, Università di Torino, Turin, Italy

2021

• Unifying Themes in Geometry, September 27-30, Lake Como School of Advanced Studies, Como, Italy
• Summer School and Conference on Six Functor Formalism and Motivic Homotopy Theory, September 20-24, Università degli Studi di Milano, Milan, Italy
• Summer school on derived and triangulated categories, September 13-17, BUW, Wuppertal, Germany
• 2021 Graduate Summer School: An introduction to motivic homotopy theory and its applications, July 12-16, IAS/PCMI, Princeton, New Jersey, USA
• Toposes online, June 24-26, 28-30, IHÉS, Bures-sur-Yvette, France
• Masterclass: Non-Archimedean Geometry Techniques in Mirror Symmetry, June 22-26, KU/UCPH, Copenhagen, Denmark
  cancelled due to Covid-19
• Bring your own coffee: K-theory and related topics, May 25-26, UofT, Toronto, Canada
• Masterclass: Scissors congruence, then and now, KU/UCPH, Copenhagen, Denmark
  cancelled due to Covid-19

2020

• Felix Klein Lectures 2020: Quiver moduli and applications, October 20-29, HCM, Bonn, Germany
• Summer school on derived and triangulated categories, September 14-18, BUW, Wuppertal, Germany
  postponed due to Covid-19
• Summer School: An introduction to the Langlands correspondence, June 15-19, Centro di Ricerca Matematica Ennio De Giorgi, Pisa, Italy
  cancelled due to Covid-19
• 2020 Summer Tropical Algebraic Geometry Online SeminAUR (STAGOSAUR): Top Weight Cohomology of Moduli Spaces of Curves, June 12-August 07
• Fifth international workshop on zeta functions in algebra and geometry, May 25-29, Laboratoire J.A. Dieudonné, Nice, France
  postponed due to Covid-19
• Western algebraic geometry online (WAGON): A virtual edition of WAGS, April 18-19
• Group theory days in Düsseldorf, January 20-21, HHU, Düsseldorf, Germany

2019

• 32nd NRW Topology Meeting, November 08-09, HHU, Düsseldorf, Germany
• Workshop: Del Pezzo surfaces and Fano varieties, July 22-26, HHU, Düsseldorf, Germany

At HHU Düsseldorf:

• De facto supervision of the Bachelor thesis "The Homogeneous Spectrum of Milnor-Witt K-theory of a Field" of E. T. Büscher
• De facto supervision of the Bachelor thesis "Model Structures on various Categories" of D. Dratschuk

In accordance with. §5 TMG:

Thor Wittich
Institut für Mathematik
Universität Osnabrück
Albrechtstrasse 28a
49076 Osnabrück