Logic Seminar- Cohesive powers of directed graphs

Time: Thursday, October 14, 4:30-5:30PM

Place: zoom

https://gwu-edu.zoom.us/j/92851328474?pwd=MVZ0Z1dnQzFaSk1oNkZ3NFQ5MklSQT09

Speaker:  Keshav Srinivasan, GWU
 

Title: Cohesive powers of directed graphs

Abstract: While typical ultrapower constructions produce uncountable models, cohesive power constructions allow us to algorithmically build countable non-standard models with interesting properties. We will present some of our recent results on cohesive powers for structures from various important classes of directed graphs. We will prove a universal embeddability result for graphs in cohesive powers of strongly locally finite graphs.  In general, by Dimitrov's theorem, only first-order properties expressed by sentences at lower levels of arithmetical hierarchy are preserved by cohesive powers. We will outline a classification of certain structures from concrete classes when the cohesive power is isomorphic to the original structure.