Dies ist die Homepage des Oberseminars "Mathematische Logik" im
Wintersemester 2011.
Heike Mildenberger.
Martin Ziegler.
Zeit und Ort
Mi 16:3018:00, SR 404 in der Eckerstr. 1, vorher Tee in Zimmer 310
 26.10.2011
Adrian Mathias
Title: The use of
ideas of Vopenka and Solovay to simplify definitions of sets of
reals.
Abstract: Scott and Myhill in the 1960s developed the notion of ordinal
definability, and defined the inner model HOD. Vopenka then showed that
every real number is generic over HOD. Solovay's analysis of Lebesgue
measurability led to the notion of an infinityBorel set of reals. The
work of the Californian Cabal on the axiom of determinacy has yielded a
proof that if V=L(R) and AD holds, then every OD set of reals is
infinityBorel with code in HOD, In this talk, I shall present in some
detail the above definitions and results, which play a pivotal role in
Woodin's proof that AD yields inner models with many Woodin cardinals.
 02.11.2011
Heike
Mildenberger
Title:
Specialising Aronszajn trees in a gentle manner
Abstract:
We show that there are proper forcings based upon
countable trees of creatures that specialise a given Aronszajn
tree and iterate these forcings with countable support. With a
strong form of halving we ensure that the Ostaszewki club holds
in the extension. This is joint work with Shelah.
 9.11.2011
kein Vortrag
 16.11.2011
Martin
Ziegler
Titel: "Die
Automorphismusgruppe des Urysohnraums"
Zusammenfassung:
Wenn man den Normalteiler der beschränkten Automorphismen
herausdividiert, ist die Automorphismengruppe einfach. Das ist
eine gemeinsame Arbeit mit Katrin Tent.
 23.11.2011
Mihai Prunescu
Title:
$F_p$affine recurrent double sequences oever $F_q$ are $p$automatic
Abstract:
A recurrent double sequence $a(m,n)$ is given by fixing two sequences $a(m,
0)$ and $a(0, n)$ as initial conditions and
a rule of recurrence $a(m,n) = f(a(m, n1), a(m1, n1), a(m1, n))$ for $m,
n \geq 1$. We show that if the sequences
are $p$automatic and have values in a finite field $F_q$ of characteristic
$p$, and if the recurrence $f$ is
$F_p$affine, then the double sequence $a(m,n)$ is $p$automatic.
Consequently all such double sequences can be defined
by matrix substitution. For the proof we show that the formal series $\sum
a(m,n) X^m Y^n$ is algebraic over the field
of rational functions $F_q(X, Y)$.
 30.11.2011
Michael Pinsker Title:
Reducts of Ramsey structures: the canonical approach
Abstract:
Consider the following problem: We are given a countably infinite
relational base structure S; the goal is to determine its reducts,
i.e., all relational structures T on the domain of S which have a
firstorder definition in S. When doing so, we identify reducts T, T'
of S when they are firstorder interdefinable.
This problem has been studied for numerous base structures S. For
example, Cameron showed that the dense linear order has 5 reducts,
Thomas proved that the random graph has 5 reducts as well, and Junker
and Ziegler found that the dense linear order with a constant has 116
reducts.
With the original goal of refining Thomas' classification of the
reducts of the random graph, Bodirsky and I developed a general method
that turns out to be applicable to a considerable class of base
structures S. For example, the method has since been used in order to
find the reducts of the random partial order (number of reducts: 5
again!) and the random trianglefree graph with a constant (number of
reducts: 13).
I will present our method and outline how it can be used in oder to
reprove Thomas' theorem.
 7.12.2011
Luca Motto Ros
The descriptive settheoretical complexity of the embeddability relation
Abstract. We investigate the complexity of the embeddability
relation on \( \mathrm{Mod}^\kappa_\varphi \), the class of models of
size $\kappa \geq \omega$ satisfying a given $\mathcal{L}_{\kappa^+
\kappa}$sentence \(\varphi\), in terms of some reducibility notions
which are very popular in descriptive settheory. In particular, we
will show that if either \( \kappa = \omega \) or \( \kappa \) is
weakly compact, then the embeddability relation is \emph{(invariantly)
universal}, i.e.\ for every analytic quasiorder \( R \) on \(
\pre{\kappa}{2} \) there is an \( \L_{\kappa^+ \kappa} \)sentence \(
\varphi \) such that \( R \) is Borel bireducible with the relation of
embeddability on \( \mathrm{Mod}^\kappa_\varphi \).

14.12.2011
Viktor Selivanov
Title: A Gandy
Theorem for Abstract Structures and Applications to FirstOrder
Definability Abstract: We establish a Gandy theorem for
a class of abstract structures and deduce some corollaries, in
particular the maximal definability result for arithmetical
structures in the class. We also show that the arithmetical
structures under consideration are biinterpretable (without
parameters) with the standard model of arithmetic. As an example
we show that for any k3 a predicate on the quotient
structure of the hquasiorder of finite klabeled forests is
definable iff it is arithmetical and invariant under
automorphisms. This structure is closely related to the
extension of the Wadge reducibility to kpartitions. There are
also other natural examples of such structures. This is a joint
work with Oleg Kudinov.
 21.12.2011
Hans Adler
Titel: Theorien ohne die Baumeigenschaft 2. Art
Zusammenfassung: Theorien ohne die Baumeigenschaft 2. Art verallgemeinern sowohl
einfache Theorien als auch Theorien ohne die
Unabhängigkeitseigenschaft. Einige Ergebnisse der letzten Zeit,
insbesondere Kim's Lemma für Theorien ohne die Baumeigenschaft 2. Art,
legen es nahe, dass man auch in diesem Kontext noch Stabilitätstheorie
treiben kann.
 11.01.2012
Riccardo Camerlo
Title: The density point property
Abstract: Some results are presented about spaces that satisfy (or do not satisfy) the
density point property. In particular, a thorough investigation is performed on the
Cantor space.
 18.01.2012
Martin Ziegler
Titel: "Generische Automorphismen von abzählbaren Strukturen"
Zusammenfassung: Wir geben einen einfachen Beweis für das
KechrisRosendahlKriterium für die Existenz von generischen
Automorphismen abzählbarer Strukturen.
 25.01.2012
JuanDiego Caycedo
Title:
Tame expansions of the real and complex fields
Abstract:
The complex field and the real ordered field are
prototypical examples of wellbehaved structures from the
modeltheoretic viewpoint, although in rather different
ways. Indeed, in both cases there is a certain geometric
understanding of definable sets. Natural questions are what
expansions of these structures introducing new definable
sets admit similar results and where is there a dividing
line between "tame" and "wild" expansions.
In the case of the real field, a rich theory has been
developed for ominimal expansions. Also, a meaningful
division is obtained when tame expansions are defined to be
those which do not define the set of integer numbers.
For expansions of the complex field, it is less clear what
the notion of tame expansions should be. In this context, I
will discuss some examples of structures related to complex
exponentiation and some relations with the real case.
 01.02.2012
kein Vortrag
 8.2.2012
Heike Mildenberger
Determiniertheit und Forcing
Mit einer Definition der Forcingrelation mittels Gewinnstrategien in einem
unendlichen Zweipersonenspiel beweisen wir den Satz von Donald Martin,
dass Delta_1^1Spiele im Raum $\lambda^\omega$ determiniert sind.
 15.02.2012
Luis Miguel Villegas Silva
Title: The twocardinal transfer problem: the
singular case
Abstract: Let κ , λ be inﬁnite cardinals, λ be singular. Let L be a ﬁrst
order countable language with at least one symbol of unary predicate
U. Let A be an Lstructure of type (κ ++ , κ ), that is, A = κ ++ and
U A  = κ . We shall prove that there exists an Lstructure B of type
(λ ++ , λ ) elementarily equivalent to A.
This problems was solved by Jensen in the late 70’s but
unfortunately
the manuscript of the proof is lost. Jensen asked me to provide a
complete proof of this case of the twocardinal transfer problem.
