Generalized Laver Diamond

Speaker: 

Sean Cox

Institution: 

Fields Institute

Time: 

Monday, November 26, 2012 - 4:00pm to 5:30pm

Host: 

Location: 

RH 440R

Laver functions for supercompact cardinals appear in many forcing constructions, including all known constructions of models of strong forcing axioms. Viale proved that the Proper Forcing Axiom implies the existence of a "generic" Laver function from $\omega_2 \to H_{\omega_2}$. I will discuss his result and some recent work of mine on generic Laver functions.

Silver's model for failure of SCH

Speaker: 

Ryan Holben

Institution: 

UCI

Time: 

Monday, October 15, 2012 - 4:00pm to 5:30pm

Host: 

Location: 

RH 440R

The classical result of Silver -- construction of the model where the Singular Cardinal Hypothesis fails -- will be presented. The emphasis is on presenting Easton suport iteration and extension of elementary embedding to a generic extension of the universe, which is the key ingredient of the entire construction.

Coding reals by clubs in $[\omega_2]^\omega$

Speaker: 

Sean Cox

Institution: 

Fields Institute

Time: 

Monday, October 8, 2012 - 4:00pm to 5:30pm

Host: 

Location: 

RH 440R

In the 80s Gitik proved the following theorem: For every real $x$ and every club $D \subseteq [\omega_2]^\omega$, there are $a,b,c \in D$ such that $x \in L(a,b,c)$. An immediate corollary of Gitik's theorem is: if $W$ is a transitive $ZF^-$ model of height at least $\omega_2$ such that $W$ is missing some real, then the complement of $W$ is stationary in $[\omega_2]^\omega$ (Velickovic strengthened Gitik's Theorem to show that the complement of such a $W$ is in fact projective stationary, not just stationary). I will present Gitik's proof and, if time permits, discuss some recent applications due to Viale and me.

A hierarchy of supercompactness measures in ZF+DC

Speaker: 

Nam Trang

Institution: 

UC Berkeley

Time: 

Thursday, May 24, 2012 - 4:00pm

Host: 

Location: 

RH 340P

For each \alpha < \omega_1, let

X_\alpha = \{f : \omega^\alpha \rightarro\powerset_{\omega_1}(\mathbb{R})| f is increasing and continuous}

and \mu_\alpha be a normal fine measure on X_\alpha. We identify X_0 with \powerset_{\omega_1}(R). Martin and Woodin independently showed that these measures exist assuming (ZF + DC_\mathbb{R}) + AD + Every set is Suslin (\mu_0's existence was originally shown by Solovay from AD_\mathbb{R}). We sketch the proof of the derived model construction giving the existence of these measures (+ AD^+) from large cardinals and the Prikry forcing construction which gives back the exact large cardinal strength from AD^+ and the measure. If time allows, we will survey some theorems on the structure theory of the model L(\mathbb{R},\mu_\alpha) assuming the model satisfies \Theta > \omega_2 and \mu_\alpha is a normal fine measure on X_\alpha. Here the main theorem is that our assumption implies L(\mathbb{R},\mu_\alpha) satisfies AD^+

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