Definable Valuations Induced by Definable Subgroups

Abstract

In his unpublished preprint "Definable Valuations" Koenigsmann shows that every field that admits a t-henselian topology is either real closed or separably closed or admits a definable valuation inducing the t-henselian topology. To show this Koenigsmann investigates valuation rings induced by certain (definable) subgroups of the field. The aim of this paper, based on the authors PhD thesis, is to look at the methods used in the preprint in greater detail and correct a mistake in the original paper based on a paper of Jahnke and Koenigsmann.