## Speaker:

Chris Laskowski

## Institution:

University of Maryland

## Time:

Monday, February 4, 2019 - 2:00pm

## Location:

340N RH

In first order logic, the Baldwin-Lachlan characterization of $\aleph_1$-categorical

theories implies that the notion is absolute between transitive models of set theory.

Here, we seek a similar characterization for having a unique atomic model of size $\aleph_1$.

At present, we have several conditions that imply many non-isomorphic atomic models of size $\aleph_1$.

Curiously, even though the results are in ZFC, their proofs rely on forcing.

This is joint work with John Baldwin and Saharon Shelah.