Absorbed Types and Derivations in Exponential o-Minimal Theories

Abstract

I analyze $\mathcal{O}$-weakly immediate and $\mathcal{O}$-residual types in an o-minimal expansion of an ordered field $\mathbb{E}$, where $\mathcal{O}$ is a convex valuation ring. The main result is a characterization of those exponential theories $T$ such that for all $(\mathbb{E}, \mathcal{O})\models T_{\mathrm{convex}}$ the image of any $\mathcal{O}$-weakly immediate type is given by some composition of translations, sign changes and exponential, of some \emph{possibly different} $\mathcal{O}$-weakly immediate type. I call these theories \emph{transserial} and they encompass simply exponential theories such as $T_{\exp}$ and $T_{an, \exp}$. A consequence of the analysis is that there are no counterexamples to \emph{Tressl's signature-alternative} (cf [15]) in models of transserial theories admitting an Archimedean prime model. The characterization has at its core some arguments that use very few but fundamental properties of the valued differential field of germs at a cut in an o-minimal structure. These are abstracted in some conditions of compatibility between the derivation and the order or the derivation and the valuation, both ultimately stemming from the mean-value-theorem in o-minimal structures. I develop some basic theory around these notions and observe that in the case of few constants (i.e.\ when the valuation ring contains the constants) these notions specialize to notions thoroughly studied in arXiv:1509.02588