Representation Theory Seminar

ABSTRACT: Many people believe that the machinery of the derived category is too technical, and is easily avoidable in studying singular spaces. In the first two talks, we looked at a problem on Betti numbers of Milnor fibers for one-dimensional hypersurface singularities, and a problem on Betti numbers of the complex and real links of an isolated complete intersection singularity; these problems are formidable without the derived category, and are mere exercises once one knows basic results about perverse sheaves and Verdier dualizing. In this final talk, we will look at a problem on local systems on complements of hyperplane arrangements, and generalize the important deletion-restriction long exact sequence.