Skript Gewöhnliche Darstellung endlicher Gruppen dvi ps pdf (Version 31.07.13)

Vorlesung in Stuttgart, SS 11
Skript Computeralgebra dvi ps pdf (Version 19.04.12)

Vorlesung in Stuttgart, WS 10/11
Skript Mathematik für Wirtschaftswissenschaftler dvi ps pdf (Version 14.10.12)

Vorlesung in Stuttgart, Teil I WS 10/11, Teil II SS 11, Teil I WS 11/12
Anleitung Computerpraktikum dvi ps pdf (Version 18.11.11)

Computerpraktikum in Stuttgart (erster von 3 Blöcken), WS 10/11
Skript Liealgebren dvi ps pdf

Vorlesung in Stuttgart, SS 10; Vorlesung in Stuttgart, SS 14.
Skript Homologische Algebra dvi ps pdf (Version 19.11.13)

Vorlesung in Bremen, WS 09/10; Vorlesung in Stuttgart, SS 10.
Skript Topologie dvi ps pdf (Version 18.11.10, sin_x_inv.eps)

Vorlesung in Koblenz, SS 09.
Skript Galoistheorie dvi ps pdf (Version 27.07.12)

Vorlesung in Koblenz, WS 08/09.
Skript Cohomologie von Gruppen dvi ps pdf (Version 18.11.13)

Vorlesung in Aachen, SS 05, fortgesetzt WS 05/06.
Einfachheit von PSL dvi ps pdf

Proseminarvortrag in Aachen, WS 04/05
Skript Lineare Algebra für Informatiker dvi ps pdf (Version 23.06.14)

Vorlesung in Ulm, WS 02/03 und WS 03/04.

A counterexample on nilpotent endomorphisms in triangulated categories dvi ps pdf

We give a counterexample to an assertion on nilpotent endomorphisms of degree 3 in triangulated categories. Roughly speaking, it is in general not possible to lower the nilpotency degree by passing to a certain cone.
(jt. w. Theo Bühler) Some elementary considerations in exact categories dvi ps pdf (Version 02.07.14)

We give counterexamples to some elementary assertions in exact categories and derive some lemmata directly from the axioms.
Dweak squares in Heller triangulated categories dvi ps pdf

We discuss a compatibility between distinguished weak (dweak) squares with the shift functor, which holds in a closed Heller triangulated category. It can be formulated in a Verdier triangulated category as well, but I do not know whether it can be proven there.
Remarks on the axioms for exact categories: (Ex 2) is redundant; if idempotents split, then first to pure mono is pure mono dvi ps pdf

The axiom (Ex 2) in the axiomatisation of exact categories as in "Heller triangulated categories" dvi ps pdf, §A.2, is redundant. Moreover, if idempotents split, then the first morphism in a composition yielding a pure monomorphism, is purely monomorphic.
A construction principle for Frobenius categories dvi ps pdf

This is a supplement to "Heller triangulated categories" dvi ps pdf. We exhibit a structure of a Frobenius category on a category of diagrams appearing in loc. cit., using a general principle.
A relative Yoneda Lemma dvi ps pdf

We construct set-valued right Kan extensions via a relative Yoneda Lemma.
On the center of the derived category dvi ps pdf

Rickard observed that in general, the center of the bounded derived category of a ring is strictly bigger than the center of the ring (unpublished). We give a simple example.


Auflösungen (Antrittsvorlesung Stuttgart) pdf, Slides dazu pdf

Heuristics concerning primes, following Greg Martin pdf

We give an integral variant of Greg Martin's heuristic argument for the asymptotic behaviour of the number of primes.
Does "Quillen A with an extra direction" hold? dvi ps pdf

The assertion in question is a bicategorical version of Quillen A, where in the "new" direction "nothing happens". I do not know whether it holds or not. I also sketched an idea how one might approach this question. I would be grateful for arguments, counterexamples (also to that idea), references, for anything.