I gave a talk in the Oberseminar mathematische Logik at the University of Bonn on January 14, 2020.

*Infinite decreasing chains in the Mitchell order*

*Abstract:* It is known that the behavior of the Mitchell order substantially changes at the level of rank-to-rank extenders, as it ceases to be well-founded. While the possible partial order structure of the Mitchell order below rank-to-rank extenders is considered to be well understood, little is known about the structure in the ill-founded case. We make a first step in understanding this case by studying the extent to which the Mitchell order can be ill-founded. Our main results are (i) in the presence of a rank-to-rank extender there is a transitive Mitchell order decreasing sequence of extenders of any countable length, and (ii) there is no such sequence of length $\omega_1$. This is joint work with Omer Ben-Neria.

As this is a blackboard talk there are no slides available, you can find a preprint related to this talk here.