#
Classification theory for abstract elementary classes

July 17 to July 21, 2006
at the

American Institute of Mathematics,
Palo Alto, California

organized by

Rami Grossberg and Monica VanDieren

## Original Announcement

This workshop will focus on
Shelah's categoricity conjecture for abstract elementary classes.
Thirty years ago Saharon Shelah proposed a far reaching program of extending
first-order classification theory for non-elementary classes. He proposed a
conjecture as a test-case for measure of development of the theory:
**Conjecture 1 (Categoricity for ***L*_{ω1,ω}).
* Let ψ be a
sentence.
If ψ is categorical in a cardinal >ב*_{ω1} then ψ is
categorical in all cardinals >ב_{ω1}.

A few years later Shelah introduced the notion of Abstract Elementary Class
(AEC) which is a semantic generalization of *L*_{ω1,ω}(Q) and
generalized the categoricity conjecture:

**Conjecture 2 (Categoricity for AECs).**
* Let **K* be an AEC. There
exists a cardinal μ(*K*) such that
categoricity in a cardinal greater than μ(*K*) implies
categoricity
in all cardinals greater than μ(*K*). Furthemore,
μ(*K*) is conjectured to be the Hanf number of *K*.

Despite significant partial results by several people, even Conjecture 1
is
still open. In recent years much progress was made on different aspects of
Shelah's original program and several intriguing connections with classical
fields of mathematics were discovered. This workshop will be dedicated to
discussion of the present state of the conjectures as well as the broader
program of developing a classification theory for AECs. Also several
examples and applications will be discussed.

## Material from the workshop

A list of participants.
The workshop schedule.

A report on the workshop activities.

Talk by Meeri Kesala.