The Leading Ideal of a Complete Intersection of Height Two in a 2-Dimensional Regular Local Ring
Titel:
The Leading Ideal of a Complete Intersection of Height Two in a 2-Dimensional Regular Local Ring
Auteur:
Goto, Shiro Heinzer, William Kim, Mee-Kyoung
Verschenen in:
Communications in algebra
Paginering:
Jaargang 36 (2008) nr. 5 pagina's 1901-1910
Jaar:
2008-05
Inhoud:
Let (S,) be a 2-dimensional regular local ring and let I = (f, g) be an ideal in S generated by a regular sequence f, g of length two. Let I* be the leading ideal of I in the associated graded ring gr(S), and set R = S/I and = /I. In Goto et al. (2007), we prove that if μG(I*) = n, then I* contains a homogeneous system {ξi}1≤i≤n of generators such that deg ξi + 2 ≤ deg ξi+1 for 2 ≤ i ≤ n - 1, and htG(ξ1, ξ2,…, ξn-1) = 1, and we describe precisely the Hilbert series H(gr(R), λ) in terms of the degrees ci of the ξi and the integers di, where di is the degree of Di = GCD(ξ1,…, ξi). To the complete intersection ideal I = (f, g)S we associate a positive integer n with 2 ≤ n ≤ c1 + 1, an ascending sequence of positive integers (c1, c2,…, cn), and a descending sequence of integers (d1 = c1, d2,…, dn = 0) such that ci+1 - ci > di-1 - di > 0 for each i with 2 ≤ i ≤ n - 1. We establish here that this necessary condition is also sufficient for there to exist a complete intersection ideal I = (f, g) whose leading ideal has these invariants. We give several examples to illustrate our theorems.