The possible extremal Betti numbers of a homogeneous ideal
arXiv:1111.0442
Abstract
We give a numerical characterization of the possible extremal Betti numbers (values as well as positions) of any homogeneous ideal in a polynomial ring over a field.
To appear in Proc. Amer. Math. Soc.. Changed title and abstract from the previous version. Essentially, this version (which is the one that will be published in PAMS) differs from the previous one because the removal of the first part, that has however been enclosed in the new article of the same three authors entitled "An intriguing ring structure on the set of d-forms"