Dies ist die Homepage des Oberseminars "Mathematische Logik" im
Sommersemester 2013.
Heike Mildenberger.
Martin Ziegler.
Zeit und Ort
Mi 16:3018:00, SR 404 in der Eckerstr. 1, vorher
ab kurz nach 4 Tee in Zimmer 310
Vorträge
 17.4.2013
Luis Miguel Villegas Silva
The principle Diamond Star
Abstract: In this talk we shall present the combinatorial principle diamond(k) star. It is
stronger than usual diamond(k). It is known that
in L, diamond(k) star holds iff k is not ineffable. We will sketch the proof that diamond(k) star
holds when k is a limit cardinal not ineffable, under GCH.
 24.4.2013
Martin Ziegler Pseudoräume
 1.5.2013
holiday
http://de.wikipedia.org/wiki/Erster_Mai
 8.5.2013
Regula Krapf
The pseudointersection number and the tower number
 15.5.2013
Adrian Mathias
Unsound Ordinals
An ordinal zeta is *unsound* if there are subsets A_n (n in omega) of
it such that as b ranges through the subsets of omega, uncountably many
ordertypes are realised by
the sets $\bigcup_{n \in b} A_n$.
Woodin in 1982 raised the question whether unsound ordinals
ordinals exist; the answer I found then (to be found in a paper
published in the Mathematical Proceedings of the Cambridge Philosophical Society volume 96 (1984) pages 391411) is this:
Assume DC. Then the following are equivalent:
i) the ordinal $\omega_1^{\omega + 2}$ (ordinal exponentiation) is unsound
ii) there is an uncountable wellordered set of reals
That implies that if omega_1 is regular and the ordinal
mentioned in i) is sound, then omega_1 is strongly inaccessible in the
constructible universe. Under DC, every
ordinal strictly less than the ordinal mentioned in i) is sound.
There are many open questions in this area: in particular, in
Solovay's famous model where all sets of reals are Lebesgue measurable,
is every ordinal sound ? The question may be delicate, as Kechris and
Woodin have shown that if the Axiom of Determinacy is true then there
is an unsound ordinal less than omega_2.
 22.5.2013
Pfingstpause
 29.5.2013
Heike Mildenberger
Resurrecting Ramsey ultrafilters
Suppose we have a Ramsey ultrafilter $V$ in the ground model
and another, nonnearly coherent $P$point $E$.
Is there a forcing that destroys $V$, preserves $E$ (and hence $\aleph_1$),
such that in the generic extension $V$ can be complemented to
a Ramsey ultrafilter again?
Using work by Blass (1987) and Eisworth (2002) and of my own
we show that there is a forcing that destroys $V$, keeps $E$, and
forces that in the extension $V^+$, the set of $V$positive sets,
is a selective coideal. Then we can cite
a proposition of Adrian Mathias (Happy Families, Annals of Math. Log (1977))
and get in the extension a Ramsey ultrafilter $V_1 \subseteq V^+$.
I will also explain the purpose of such technical work.
 5.6.2013
Giorgio Laguzzi
Generalized random forcing for weakly compact When dealing with the generalized Cantor space 2^\kappa, for \kappa
regular uncountable, the notion of Cohen forcing and Baire property trivially
generalizes. What is more complicated to do is to find a right generalization
of random forcing, since the usual notion of Lebesgue measure does not
generalizes straightforwardly. During the talk, we present Shelah's recent
result shedding light on this problem, by introducing a forcing which is
simultaneously \kappa^+cc and \kappa^\kappabounding, for \kappa weakly
compact.
 12.6.2013
Jörg Flum
On Limitations of the EhrenfeuchtFraïssé method
EhrenfeuchtFraïssé games and their generalizations have been
quite successful in finite
model theory and yield various inexpressibility results. However, for key
problems such as the P NP problem no progress has been
achieved using the games. We show that for these problems it is already
hard to get the board for the corresponding EhrenfeuchtFraïssé
game. We obtain similar
results for the socalled AjtaiFagin games and for a variant where the
structures are obtained randomly.
 19.6.2013
Markus Junker Heyting algebras
 26.6.2013
Menachem Magidor
Inner Models for Set Theory Defined by
Generalized Logics
pdf file of the abstract
 3.7.2013
Misha Gavrilovich
A categorytheoretic viewpoint on first definitions in general topology
We observe that several definitions in a first course on general topology, such as Hausdorff,
dense, T_0, T_1, admit an easy reformulation as computations with partial preorders of
categorytheoretic nature. Namely, these computations correspond to rules for manipulating
commutative diagrams involving only finite topological spaces as constants (and variables). We
suggest a calculus based on these rules.
 10.7.2013
Juan Diego Caycedo
The real field with dense subgroups of the torus
 17.7.2013
Fourth European Set Theory Conference, Barcelona
