Valued Modules over Skew Polynomial Rings 2

Following our first article, we continue to investigate ultrametic modules over a ring of twisted polynomials of the form $[K;\text{vfi}]$, where $\text{vfi}$ is a ring endomorphism of $K$. The main motivation comes from the the theory of valued difference fields (including characteristic $p>0$ valued fields equipped with the Frobenius endomorphism). We introduce the class of modules, that we call, affinely maximal and residually divisible and we prove (relative -) quantifier elimination results. Ax-Kochen & Erhov type theorems follows. As an application, we axiomatize, as a valued module, any ultraproduct of algebraically closed valued fields $($\mathbb{F}${p^n}(t)^{alg}){n\in $\mathbb{N}$}$,offixedcharacteristic$p>0$,eachequippedwiththemorphism$x\mapsto x^{p^n}$andwiththe$t$-adic valuation.