Title: Effective Ultraproducts and Their Applications
Speaker: Rumen Dimitrov, Western Illinois University
Date and Time: Thursday February 8, 12:30-1:30
Place: Phillips Hall (801 22nd Street), Room 730
Abstract: We use cohesive (effectively indecomposable) sets to build nonstandard versions of the field of rational numbers. We study the isomorphism types of these models when the complements of the cohesive sets are computably enumerable. Using Koenigsmann’s work on Hilbert's Tenth Problem we give a new proof that these fields are rigid.