5:00PM: The Semigroup of Betti Diagrams
Daniel ErmanA string of recent papers by Boij/Soederberg, Eisenbud/Schreyer, and Eisenbud/Floystad/Weyman provides an elegant description of the rational cone of Betti diagrams of modules. These results give remarkable structure theorems on the minimal free resolution of a graded module. To obtain a complete description of all possible minimal free resolutions, one must consider not only the cone of Betti diagrams, but the underlying semigroup of Betti diagrams as well. I will discuss what is known and what is not known about this semigroup.