Guest lecture on March 11th, 2026 by Zixuan Zhu

Title: Rank and Independence of Imaginaries in Proper Pairs of ACF

Abstract: Let $T_P$ be the theory of beautiful pairs of algebraically closed fields of fixed characteristic. It is known that for real tuples in models of $T_P$, SU-rank coincides with Morley rank and can be computed effectively.

Building on Pillay’s geometric description (2007) of imaginaries in $T_P$, we define an additive rank on imaginaries of $T_P$, called the geometric rank. It takes values in $\omega\cdot\mathbb{N}+\mathbb{Z}$ and coincides with SU-rank on real tuples. It refines SU-rank and characterizes forking in $T_P^\text{eq}$. As a consequence, we derive an explicit criterion for determining forking independence.