Marilena Crupi. Source: Journal of Commutative Algebra, Volume 12, Number 1, 53--70.Abstract:
Let [math] be a polynomial ring in [math] variables over a field [math] of any characteristic. Let [math] be a strongly stable submodule of a finitely generated graded free [math] -module [math] , with all basis elements of [math] of the same degree. The existence of a general strongly stable submodule [math] of a finitely generated graded free [math] -module [math] , [math] , which preserves values and positions of the extremal Betti numbers of  [math] , is proved.