## "A world from a sheet of paper". Hirzebruch lecture by Tadashi Tokieda on Wednesday, October 31, University Club Bonn

Starting from just a sheet of paper, by folding, stacking, crumpling, tearing, we will explore a rich variety of phenomena, from magic tricks and geometry to elasticity and the traditional Japanese art of origami. Much of the lecture consists of actual table-top demos, which you can try later with friends and family.

Professor **Tadashi Tokieda** is a professor of mathematics at Stanford University. He grew up as a painter in Japan, became a classical philologist in France, and has been an applied mathematician in the US and Europe. He is active in outreach in the developing world, especially via the African Institute for Mathematical Sciences.

## New guests at the MPIM

## Introductory talks in topology

## Introductory talks in topology

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## Quest for D-Affinity

I am interested in the following problem: "classify all smooth connected D-affine projective varieties".

As a part of their proof of Kazhdan-Lusztig Conjecture, Beilinson and Bernstein have proved that

the partial flag varieties G/P are D-affine. This is the current state of art: no other examples are known

but there is no proof that the G/P-s exhaust all the possible examples.

In my talk I will show that in three natural classes of varieties D-affinity implies that the variety is G/P,

review some examples of more general D-affine spaces, and try to convince the listeners that the problem

is related to some other interesting questions in Algebraic Geometry.

## Symmetric matrices associated with oriented link diagrams.

Motivated by metaplectic invariants of Goldschmidt–Jones,

generalizing the cyclotomic invariants of Kobayashi–Murakami–Murakami,

I will explain a construction which associates to each oriented link

diagram a symmetric matrix with elements being quadratic polynomials

in one indeterminate with integer coefficients. Based on a slightly

modified S-equivalence of Trotter and Murasugi in the space of

symmetric matrices, the construction gives rise to an invariant

of oriented links. In particular, the signature of the matrix is

conjecturally related to the Tristram–Levine signature function.

## Warps and grids for double and triple vector bundles

## What is an Einstein metric?

## What is a Berkovich space?

## What is a Teichmüller polynomial?

## "What is...?" seminar

## Belyi's theorem/dessin d'enfant

## Presentation of number theory aspects of Ihara's paper

## Dinner at Gasthaus "zum Stiefel"

We have arranged a dinner for Thursday evening at 7 pm in the Kaminzimmer at "Im Stiefel".

The price will be 40 EUR per person.

Further information will follow.

## Propagators of the wave equation on low regularity spacetimes

In this talk, I will define the classical and non-classical of the wave equation.

Also, I will give some motivations about why low regularity scenarios are interesting.

Finally, I will focus on the classical ones and its relationship with Quantum Field Theory in spacetimes with limited regularity.

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