A New Kim's Lemma

Abstract

Kim's Lemma is a key ingredient in the theory of forking independence in simple theories. It asserts that if a formula divides, then it divides along every Morley sequence in type of the parameters. Variants of Kim's Lemma have formed the core of the theories of independence in two orthogonal generalizations of simplicity - namely, the classes of NTP2 and NSOP1 theories. We introduce a new variant of Kim's Lemma that simultaneously generalizes the NTP2 and NSOP1 variants. We explore examples and non-examples in which this lemma holds, discuss implications with syntactic properties of theories, and ask several questions.