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Fakultät für Mathematik Universität Regensburg
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Simple homotopy theory and manifold topology
Semester
SoSe 2026

Lecturer
Marco Volpe

Type of course (Veranstaltungsart)
Seminar

German title
Einfache Homotopietheorie und Topologie von Mannigfaltigkeiten

Contents
Broadly speaking, simple homotopy theory studies the combinatorial aspects of algebraic topology.
More specifically, a map between finite CW complexes is called a simple homotopy equivalence if it
can be written as a finite composition of elementary expansions and collapses. A natural question is
whether every homotopy equivalence is of this form. In general, the answer is no, and the failure of
a homotopy equivalence to be simple is measured by the Whitehead torsion. The torsion takes values
in the Whitehead group, a K-theoretic object that depends only on the fundamental group. Simple
homotopy theory has been successfully applied in manifold topology. For example, work of Turaev and
others shows that two orientable closed 3-manifolds are homeomorphic if and only if they are simple
homotopy equivalent. In high dimensions, simple homotopy theory provides a criterion for determining
when an h-cobordism is trivial, known as the s-cobordism theorem. In this seminar, we will give
an introduction to simple homotopy theory and discuss some of its applications to manifold topology.
Time permitting, and depending on the background and interests of the participants, we may also
discuss Waldhausen’s more modern approach to the subject.

Literature
Cohen: A course in simple homotopy theory. Lurie: Algebraic K-theory and manifold topology. More
references and a seminar program will appear in the website of the seminar.

Recommended previous knowledge
Algebraic topology: CW-complexes, homotopy groups, universal covering, singular/cellular homology.
Some familiarity with commutative algebra. Some familiarity with differential topology. Based on the
prerequisites of the participants, we may have a couple of talks where we review some of the above.

Time/Date
Wednesday 16-18

Location
M009

Additional question session
Time/Date: Decided individually with each speaker
Location: M228

Course homepage
https://sites.google.com/view/marco-volpe/seminars/simple-homotopy-theory-and-manifold-topology
(Disclaimer: Dieser Link wurde automatisch erzeugt und ist evtl. extern)

Registration
  • Organisational meeting/distribution of topics: Two weeks before the beginning of the semester,
    or by email.
  • Registration for course work/examination/ECTS: FlexNow
Course work (Studienleistungen)
  • Presentation: Giving a seminar talk of roughly 90 minutes
Examination (Prüfungsleistungen)
  • Detailed written report of the seminar talk
Modules
BSem, MV, MSem, LA-GySem

ECTS
4.5