Some Remarks on Kim-dividing in NATP Theories

TL;DR

This paper proves that Kim-dividing over models in NATP theories can be witnessed by coheir Morley sequences, establishing key properties and conditions related to Kim-forking and Kim-dividing in this class of theories.

Contribution

It demonstrates that Kim-dividing over models in NATP theories is always witnessed by coheir Morley sequences and explores related conditions and corollaries.

Findings

Kim-dividing over models is witnessed by coheir Morley sequences in NATP theories.

If a formula Kim-forks over a model, then it quasi-divides over the same model.

In NATP theories, certain conditions characterize witnesses of Kim-dividing.

Abstract

In this note, we prove that Kim-dividing over models is always witnessed by a coheir Morley sequence in NATP theories. Following the strategy of Chernikov and Kaplan [8], we obtain some corollaries which hold in NATP theories. Namely, (i) if a formula Kim-forks over a model, then it quasi-divides over the same model, (ii) for any tuple of parameters $b$ and a model $M$, there exists a global coheir $p$ containing $\text{tp}(b/M)$ such that $B \ind^K_M b'$ for all $b'\models p|_{MB}$. We also show that for coheirs in NATP theories, condition (ii) above is a necessary condition for being a witness of Kim-dividing, assuming that a witness of Kim-dividing exists (see Definition 4.1 in this note). That is, if we assume that a witness of Kim-dividing always exists over any given model, then a coheir $p\supseteq \text{tp}(a/M)$ must satisfy (ii) whenever it is a witness of Kim-dividing of $a$ over a model $M$. We also give a sufficient condition for the existence of a witness of Kim-dividing in terms of pre-independence relations. At the end of the paper, we leave a short remark on Mutchnik's recent work [16]. We point out that the class of $\omega$-NDCTP$_2$ theories, a subclass of the class of NATP theories, contains all NTP$_2$ theories and NSOP$_1$ theories. We also note that Kim-forking and Kim-dividing are equivalent over models in $\omega$-NDCTP$_2$ theories, where Kim-dividing is defined with respect to invariant Morley sequences, instead of coheir Morley sequences as in [16].