Bonn Mathematical Logic Group

Oberseminar mathematische Logik


Time and location

Monday 16.30-18.00 in room 1.007, Endenicher Allee 60.

The participants of the seminar are welcome for coffee and tea in the Hausdorff-Raum 1.012 at 16.00 before the talks.


Advanced talks on mathematical logic by guests and members of the logic group.


15 October  Philipp Lücke Free groups and automorphism groups of infinite fields
Abstract Slides
22 October  Philipp Schlicht Perfect subsets of generalized Baire spaces
29 October  Stefan Geschke An induced Ramsey theorem for clopen graphs
We use forcing to prove Ramsey theorems for colorings of closed subsets of large clopen graphs.
5 November David Schrittesser (Wien) Separating ideals and Jensen Coding with Easton Support
3 December Dominik Adolf (Universität Münster) The strength of PFA(aleph_2) plus a precipitous Ideal on omega_1
We will present an argument for extracting strength from the above mentioned hypothesis building on a work of Claverie and Schindler. We will give a short overview of the inner model theory used with a focus on showcasing the core ideas underpinning our methods. We will discuss limitations of the argument and ideas on how to overcome them.
5 December  (Wednesday) Zum Dies Academicus trägt Peter Koepke um 15.15 Uhr im Hörsaal IV im Hauptgebäude vor: Berechenbarkeit und ihre Grenzen - zum 100. Geburtstag von Alan Turing
17 December  Luca Motto Ros (Universität Freiburg) The embeddability relation on models of size kappa is (strongly) invariantly universal when kappa^{<kappa}=kappa
07 January Marcin Sabok (Polish Academy of Sciences, Warsaw) A dichotomy in canonization of analytic equivalence relations
I will show and discuss a dichotomy that occurs in attempts of canonization of analytic equivalence relations. The dichotomy says that under suitable minimality condition for P_I, if E is an analytic equivalence relation on a Polish space, then - either there is a Borel I-positive set which consists of E-independent elements (i.e. E canonizes to the identity) - or there is a Borel I-positive set such that E|B is I-ergodic (this means the saturations of every two Borel I-positive subsets of B have nonempty intersection ) I will present some typical examples for both types of behavior and sketch a proof of the dichotomy. The proof will use suitably chosen generic ultrapowers. This is joint work with Vladimir Kanovei and Jindra Zapletal.
14 January  Anne Fernengel On the Continuum Function in ZF
We show that in Zermelo-Fraenkel set theory without the Axiom of Choice, a surjectively modified continuum function can take almost arbitrary values.
21 January  Mona Rahn will give a talk in the Master student's seminar (16.30 in room 1.007): Hat games without the axiom of choice
Consider the following game: omega many people named 0, 1, 2, . . . sit in a row, where person n sees every person with a greater number, namely n+1, n+2, etc. Each person wears a hat that has a color taken from a fixed set of colors. Starting with the person who sees all the others, the people guess the color of their hats, one after the other. The people are allowed to agree on a strategy beforehand but are not allowed to communicate once they wear their hats. However, they do hear the previous guesses. Surprisingly, assuming the Axiom of Choice, there is always a strategy that guarantees that at most one person guesses his hat wrong. We investigate what happens when we let go of the Axiom of Choice. We present a model of ZF showing that AC is necessary in order to find the aforementioned strategies for at most countable sets of colors. This is due to the fact that the existence of those strategies implies, among other things, the existence of a set of reals without the Baire property and a subset of [omega]^omega that is not Ramsey.
28 January  Lutz Strüngmann (Hochschule Mannheim) Endomorphisms of aleph_n-free modules over the p-adic intergers
07 February  Thursday 14.15-15.45 Daisuke Ikegami (Berkeley) tba



Last changed: 22 January 2013