Strongly NIP almost real closed fields

The following conjecture is due to Shelah-Hasson: Any infinite strongly NIP field is either real closed, algebraically closed, or admits a non-trivial definable henselian valuation, in the language of rings. We specialise this conjecture to ordered fields in the language of ordered rings, which leads towards a systematic study of the class of strongly NIP almost real closed fields. As a result, we obtain a complete characterisation of this class.Comment: To appear in MLQ Math. Log. Q. A previous version of this preprint was part of arXiv:1810.10377. arXiv admin note: text overlap with arXiv:2010.1183

DEFINABLE SETS IN DP-MINIMAL ORDERED ABELIAN GROUPS (Model theoretic aspects of the notion of independence and dimension)

This article surveys some recent results on ordered abelian groups (possibly with additional definable structure) from the subclass of NIP theories which are dp-minimal. To put these results in context, the first part of the article reviews and compares various other generalizations of a-minimality (such as local a-minimality and a-stability) and their consequences. It is useful to make the further assumption that there is a cardinal bound on the number of convex subgroups definable in elementary extensions of the structure. Under this hypothesis, some classic theorems on o-minimal structures, such as the monotonicity theorem for unary definable functions, can be suitably generalized

Vapnik-Chervonenkis density in some theories without the independence property, I

We recast the problem of calculating Vapnik-Chervonenkis (VC) density into one of counting types, and thereby calculate bounds (often optimal) on the VC density for some weakly o-minimal, weakly quasi-o-minimal, and $P$-minimal theories.Comment: 59