The Koszul Homology of an Ideal

Recently many researchers have worked on problems connected with various graded algebras associated to an ideal I in a local ring R. Two algebras in particular have received the most attention: the associated graded algebra of Z, gr,( R) = R/Z@ Z/Z’@ ... , and the Rees algebra of Z, defined to be R[Zt]. Brodmann [2] and Goto and Shimoda [9] have studied the local cohomology of R[Zr] for certain primary ideals Z, Herzog has obtained new results in the case where Z is the maximal ideal, Eisenbud and Huneke [7] studied the CohenMacaulayness of these algebras, while the concepts of d-sequences [ 111 and Hodge algebras [S] have been used to understand these graded algebras. Recently Simis and Vasconcelos w, 211 related the Cohen Macaulayness, torsion-freeness, and normality of these algebras to the Koszul homology of I. If Z is an ideal, we let ZZ,(Z; R) denote the jth Koszul homology of the ideal Z with respect to somejixed system of generators for I. We denote the symmetric algebra of a module A4 by Sym(M), and denote thejth graded piece of this algebra by Sym,(M). In [20] and [21] Simis and Vasconcelos construct a complex A’(Z) (or simply A) with the following properties: