Junior Number Theory Seminar

The goal is to describe Ribet's lemma which describes a way to construct cohomology classes from group representations. We show the first application of this; the Herbrand-Ribet Theorem. The approach is to reformulate the problem in terms of the existence of a certain cohomology class, and to construct such a class from the Galois Representation tied to an appropriate modular form, using Ribet's Lemma