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A New Kim's Lemma

Alex Kruckman and Nicholas Ramsey

Vol. 3 (2024), No. 3, 825–860
DOI: 10.2140/mt.2024.3.825
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 NTP 2 and NSOP 1 theories. We introduce a new variant of Kim’s Lemma that simultaneously generalizes the NTP 2 and NSOP 1 variants. We explore examples and nonexamples in which this lemma holds, discuss implications with syntactic properties of theories, and ask several questions.

Keywords
classification theory, forking, dividing, Kim-dividing
Mathematical Subject Classification
Primary: 03C45
Milestones
Received: 16 September 2023
Revised: 2 April 2024
Accepted: 8 April 2024
Published: 12 August 2024
Authors
Alex Kruckman
Department of Mathematics and Computer Science
Wesleyan University
Middletown, CT
United States
Nicholas Ramsey
Department of Mathematics
University of Notre Dame
Notre Dame, IN
United States