I‘m currently reading Neukirchs „algebraic number theory“. In Chapter II he stated the following
9.12 Proposition The ramification group $R_\omega$ is the unique p-Sylow subgroup of the inertia group $I_\omega.$
We assume here, that L over K is Galois, where K admits a non-Archimedean valuation $v$ and L some extension $\omega$ of this $v$. My question is simple: Where does p come from? The proof says, that p is the characteristic of the residue class field of L. But does this field always have positive characteristic?
Best regards Roland