Archives of: Bonn Logic Seminar

Ralf Schindler: A Hamel basis for the reals without choice

09 January: 16.30
seminar room 0.008
Mathematisches Institut
Universität Bonn
Endenicher Allee 60

Ralf Schindler (Münster) – A Hamel basis for the reals without choice

The Cohen-Halpern-Levy model N has an infinite set of reals without a countable subset. Answering a question of D. Pincus and K. Prikry from 1975, we show that there is a Hamel basis in N. This is joint work with Liuzhen Wu and Liang Yu, inspired by earlier joint work with Mariam Beriashvili. DC fails in N, and it remains open if in the base theory ZF+DC, the existence of a Hamel basis implies that the reals can be wellordered.

Asger Törnquist: Definable maximal orthogonal families and discrete sets in forcing extensions

Thursday, September 10, 2015, 16.30
Seminar room 1.008, Mathematical Institute, University of Bonn

Speaker: Asger Törnquist (Kopenhagen)

Title: Definable maximal orthogonal families and discrete sets in forcing extensions

Assaf Rinot: Chain conditions of products

Thursday, July 9, 2015, 16.00
Seminar room 0.011, Mathematical Institute, University of Bonn

Speaker: Assaf Rinot (Bar-Ilan University)

Title: Chain conditions of products

Abstract: We shall survey the history of the study of the productivity of the k-cc in partial orders, topological spaces, and Boolean algebras. We shall address a conjecture that tries to characterize such a productivity in Ramsey-type language. For this, a new oscillation function for successor cardinals, and a new characteristic function for walks on ordinals will be proposed and investigated.

Giorgio Laguzzi: Roslanowski and Spinas dichotomies

Monday, July 14, 2014, 16.30
Seminar room 0.011, Mathematical Institute, University of Bonn

Speaker: Giorgio Laguzzi (Universität Hamburg)

Title: Roslanowski and Spinas dichotomies

Otmar Spinas: “Das Problem mit Silver Amoeba”

Monday, June 23, 2014, 16.30
Seminar room 0.011, Mathematical Institute, University of Bonn

Speaker: Otmar Spinas (Kiel)

Title: “Das Problem mit Silver Amoeba”

Abstract:

Ich werde die offene Frage eroertern, ob ein Amoeba für Silver-Forcing existiert, das keine Cohen reelle Zahlen adjungiert. In der Sprache der kardinalen Invarianten ist dies die Frage, ob konsistenterweise die Ueberdeckungszahl des mageren Ideals kleiner als die Additivitaet des Silver-Ideals ist.

Mirna Dzamonja: Embeddings of graphs with no large cliques

Monday, June 16, 2014, 16.30
Seminar room 0.011, Mathematical Institute, University of Bonn

Speaker: Mirna Dzamonja (University of East Anglia, Norwich, UK)

Title: Embeddings of graphs with no large cliques

Abstract:

We shall discuss embeddings between graphs omitting large
cliques and in particular we shall prove that for kappa singular of
cofinality kappa there is no universal graph of size kappa omitting
cliques of size kappa, just in ZFC.

Vassilis Gregoriades: A recursive theoretic view to the decomposability conjecture

Friday, May 30, 2014, 16.30
Seminar room 1.007, Mathematical Institute, University of Bonn

Speaker: Vassilis Gregoriades (Darmstadt)

Title: A recursive theoretic view to the decomposability conjecture

Abstract:

The decomposability conjecture states that every function from an analytic space to a separable metric space, for which the preimage of a Σ^0_{m+1} set is a Σ^0_{n+1} set, where m=1,2,…n, is decomposable into countably many Σ^0_{n-m+1}-measurable functions on Π^0_n domains. The aim of this talk is to present some recent results about this problem in zero-dimensional spaces. This is a joint work of Kihara and the speaker. The proofs make use of results from recursion theory and effective descriptive set theory, including a lemma by Kihara on canceling out Turing jumps and Louveau separation. We will first review the necessary material and then we will proceed to the proof of the new results. Moreover we will explain how these results can be extended from the context of zero-dimensional spaces to spaces of small inductive dimension.

Vladimir Kanovei: On the automorphisms in the Gitik-Koepke construction

Monday, May 26, 2014, 16.30
Seminar room 0.011, Mathematical Institute, University of Bonn

Speaker: Vladimir Kanovei (IPPI and MIIT, Moscow)

Title: On the automorphisms in the Gitik-Koepke construction

Joel David Hamkins: Transfinite game values in infinite chess and other infinite games

Friday, May 23, 2014, 17.00
Lipschitzsaal, Mathematical Institute, University of Bonn

Speaker: Joel David Hamkins (CUNY)

Title: Transfinite game values in infinite chess and other infinite games

Infinity, computability, and metamathematics, May 23 -25, 2014

Infinity, computability, and metamathematics: Celebrating the 60th birthdays of Peter Koepke and Philip Welch”

In the year 2014, Peter Koepke and Philip Welch are celebrating their 60th birthdays, and we wish to celebrate this festive occasion with a scientific workshop in their honor. Peter has been a professor at the University of Bonn for many years; Philip was a Mercator professor in Bonn during the academic year 2002/03.

Friday, May 23

16:30 – 17:00 Coffee
17:00 – 18:00 Joel Hamkins (New York): Colloquium

Saturday, May 24

10:00 – 10:50 Joan Bagaria (Barcelona)
10:50 – 11:20 Coffee break
11:20 – 12:10 Moti Gitik (Tel Aviv)
12:10 – 14:30 Lunch break
14:30 – 15:20 Ralf Schindler (Münster)
15:20 – 15:50 Coffee break
15:50 – 16:40 Heike Mildenberger (Freiburg)
16:40 – 17:10 Coffee break
17:10 – 18:00 Arthur Apter (New York)

Sunday, May 25

10:10 – 11:00 Jörg Brendle (Kobe)
11:00 – 11:15 Coffee break
11:15 – 12:05 Bernhard Schröder (Duisburg-Essen)
12:05 – 12:10 Coffee break
12:10 – 13:00 Adrian Mathias (Reunion)

Monday, May 26

16:30 – 18:00 Vladimir Kanovei (Moscow)

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