Published online by Cambridge University Press: 11 October 2019
In this article, we functorially associate definable sets to $k$-analytic curves, and definable maps to analytic morphisms between them, for a large class of
$k$-analytic curves. Given a
$k$-analytic curve
$X$, our association allows us to have definable versions of several usual notions of Berkovich analytic geometry such as the branch emanating from a point and the residue curve at a point of type 2. We also characterize the definable subsets of the definable counterpart of
$X$ and show that they satisfy a bijective relation with the radial subsets of
$X$. As an application, we recover (and slightly extend) results of Temkin concerning the radiality of the set of points with a given prescribed multiplicity with respect to a morphism of
$k$-analytic curves. In the case of the analytification of an algebraic curve, our construction can also be seen as an explicit version of Hrushovski and Loeser’s theorem on iso-definability of curves. However, our approach can also be applied to strictly
$k$-affinoid curves and arbitrary morphisms between them, which are currently not in the scope of their setting.
The authors were supported by the ERC project TOSSIBERG (grant agreement 637027).