#
Descriptive inner model theory

June 2 to June 6, 2014
at the

American Institute of Mathematics,
Palo Alto, California

organized by

Ralf Schindler and John Steel

## Original Announcement

This workshop will be devoted to inner model
theory and descriptive set theory.
The main topics for the workshop are
- the core model induction technique,
- the analysis of the hereditarily ordinal definable sets in models of $AD$,
and
- inner models with long extenders.

How to construct canonical inner models satisfying large cardinal hypotheses has
been a central problem in pure set theory since the 1960s. In recent years,
there has been encouraging progress on two broad fronts. This workshop is
devoted to communicating and developing further the new ideas.
The first broad front concerns the construction of iteration strategies. Such
constructions can be organized by the core model induction method. Here one
combines core model theory and descriptive set theory so as to produce logically
complicated iteration strategies and scales, via an induction on their logical
complexity. The core model induction is our most powerful method for obtaining
consistency strength lower bounds, and in many important cases (for example, in
the lower bound problem for the Proper Forcing Axiom), it seems indispensable.

The core model induction method relies heavily on results which connect the
hierarchy of scaled pointclasses in determinacy models (more precisely, models
of $ZF + AD^+$) with iteration strategies and mice, via an analysis of the $HODs$ of
models of $AD^+$. Grigor Sargsyan made important progress on this problem in his
2009 Ph.D. thesis. Sargsyan's work has been further developed, and applied in
core model inductions, by several people since then. Nevertheless, the basic
theory needed here is very much unfinished.

This workshop will explore its frontier. One key test question is whether the
$HOD$ of an $AD^+$ model must always satisfy GCH; another is whether it can it
satisfy moderately strong large cardinal hypotheses, such as "there is a Woodin
limit of Woodin cardinals".

The second broad front on which there has been recent progress concerns the form
that canonical inner models take when the large cardinals hypotheses are so
strong that the embeddings associated to them must be represented by long
extenders. W. Hugh Woodin has published some dramatic results on inner models
with long extenders, in a series papers that won the Hausdorff medal of the
European Set Theory Society in July 2013. We hope to communicate some of the
recent work by Woodin and others in this area.

## Material from the workshop

A list of participants.
The workshop schedule.

A report on the workshop activities.

A list of open problems.

Papers arising from the workshop:

Equiconsistencies at subcompact cardinals