Introduction and Review of the Tame Case

Abstract

The motivation behind the material presented in these notes is the following question:- if N/K is a finite Galois extension of number fields with Galois group Γ, and if \( mathfrak{D}{\text{ and }}\mathfrak{D}N \) are the rings of algebraic integers in K and N respectively, then what can be said about \( mathfrak{D}N \) as a Γ-module? A complete answer to this would be a description of \( mathfrak{D}N \) as a module over the group ring \( mathfrak{D}\Gamma \) , but since in general \( mathfrak{D}N \) need not be free over \( mathfrak{D} \) , it is more fruitful to restrict scalars and view \( mathfrak{D}N \) as a ℤΓ-module.