The Horrocks-Mumford Bundle and the Ferrand Construction.
We study the behavior of the Horrocks-Mumford bundle FHM when restricted to a plane P2 ⊂ P4, looking for all possible minimal free resolutions for the restricted bundle. To each of the 6 resolutions (4 stable and 2 unstable) we find, we then associate a subvariety of the Grassmannian G(2,4) of planes in P4. We thus obtain a filtration of the Grassmannian, which we describe in the second part of this work.
In this paper we develop a theory of Grothendieck’s six operations of lisse-étale constructible sheaves on Artin stacks locally of finite type over certain excellent schemes of finite Krull dimension. We also give generalizations of the classical base change theorems and Kunneth formula to stacks, and prove new results about cohomological descent for unbounded complexes.
Let C be an elliptic curve and E, F polystable vector bundles on C such that no two among the indecomposable factors of E + F are isomorphic. Here we give a complete classification of such pairs (E,F) such that E is a subbundle of F.