Rank axioms and supersimplicity

TL;DR

This paper introduces axioms for foundation ranks related to dividing and forking, explores their relationships, and characterizes supersimple theories using these ranks, extending classical stability theory concepts.

Contribution

It proposes axioms for the foundation ranks SU^d and SU^f, analyzes their relationships, and characterizes supersimple theories based on these ranks, extending the framework of stability theory.

Findings

U-rank is the foundation rank of Lascar-splitting independence

Provides an alternative definition of SUd similar to U

Characterizes stable and superstable theories using non-Lascar-splitting independence

Abstract

Just as Lascar's notion of abstract rank axiomatizes the U-rank, we propose axioms for the ranks $SU^d$ and $SU^f$, the foundation ranks of dividing and forking. We study the relationships between these axioms. As with superstable, we characterize supersimple types and theories based on the existence of these ranks. We show that the U-rank is the foundation rank of the Lascar-splitting independence relationship. We also provide an alternative definition of SUd similar to the original definition of U. Finally, we check that if in the standard characterizations of simple and supersimple we change the non-forking independence for the non-lascar-splitting independence, we characterize stable and superstable.