Separation for isometric group actions and hyperimaginary independence

Abstract

. We generalize P. M. Neumann’s Lemma to the setting of isometric actions on metric spaces and use it to prove several results in continuous model theory related to algebraic independence. In particular, we show that algebraic independence satisfies the full existence axiom (which answers a question of Goldbring) and is implied by dividing independence. We also use the relation- ship between hyperimaginaries and continuous imaginaries to derive further results that are new even for discrete theories. Specifically, we show that if M is a monster model of a discrete or continuous theory, then bounded-closure in- dependence in M heq satisfies full existence (which answers a question of Adler) and is implied by dividing independence.