# Order Type vs. Isomorphism Type for Models of PA II

## Alf Dolich

### The City University of New York

I will continue to discuss work of Shelah on the problem of under what conditions can the underlying order

type of a model of PA determine its isomorphism type. In particular I will outline a proof of a theorem roughly

stating that a model, M, of PA whose underlying order exhibits a week form of rigidity has the property that any

other model of PA which is order isomorphic to M is in fact isomorphic (as models of PA) to M.

Professor Dolich (Ph.D. 2002 University of Maryland, M.A. Columbia University, B.A. University of Pennsylvania) held a VIGRE Van Vleck Assistant Professorship at the University of Wisconsin, Madison, before coming to the New York area, where he now holds an Assistant Professor position at Kingsborough CC of CUNY. Professor Dolich conducts research in model theory, simple theories, and o-minimal theories with secondary interests in algebraic geometry and set theory.