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MATHEMATICA SCANDINAVICA
Article . 2002 . Peer-reviewed
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Sequences for complexes II

Sequences for complexes. II
Authors: Christensen, Lars Winther;

Sequences for complexes II

Abstract

[For part I see ibid. 89, No. 2, 161-180 (2001; see the preceding review Zbl 1021.13014).] Let \((R,{\mathfrak m})\) be a local ring, and let \(X = X_\bullet\) be a bounded \(R\)-complex with finitely generated homology modules. The Cohen-Macaulay defect \(\text{cmd}_R X\) of \(X\) is defined by \(\text{cmd}_R X = \dim_R X - \text{depth}_R X\), and \(X\) is said to be Cohen-Macaulay if \(\text{cmd}_R X = 0\). In this section 2 of the paper supports of complexes are studied and the notion of an anchor prime ideal is introduced. A prime ideal \(p\) of \(R\) is said to be an anchor prime ideal for a bounded below \(R\)-complex \(Y\) if \(p \in \text{Supp}_R Y\) and \(\dim_{R_p}Y_p + \inf Y_p = 0\). Corollary 2.4. If \(p \in \text{Ass}_R X\) is an anchor prime ideal for \(X\), then \(\text{cmd}_{R_p} X_p = \sup X_p - \inf X_p\). Theorem 2.9. \(\dim_R X + \inf X = \inf\{ s \mid \exists a_1, \dots,a_s \text{ such that } {\mathfrak m} \text{ is an anchor prime ideal for }\) \(K(a_1, \dots,a_s;X) \}\). (\(K(\;;\;)\) is the Koszul complex.) Let \( d = \dim_R X + \inf X\). A sequence of elements \(\mathbf x = x_1, \ldots,x_d \in {\mathfrak m}\) is said to be a system of parameters for \(X\) if \({\mathfrak m}\) is an anchor prime ideal for \(K(\mathbf x;X)\), and an \(X\)-parameter sequence is part of a system of parameters for \(X\). For a bounded above complex \(Y\), we put \(z_R(Y) = z_R(H_{\sup Y}(Y))\) (the set of zero divisors). A sequence of elements \(\mathbf y = y_1, \ldots,y_n\) is said to be a \(Y\)-sequence if (i) \(y_j \notin z_R K(\mathbf y_{j-1};Y)\) for \(1 \leq j \leq n\), (ii) \(K(\mathbf y;Y) \not\simeq 0\) or \(Y \simeq 0\). In section 3, several theorems concerning \(X\)-parameter sequences and the Cohen-Macaulay defect are shown, and the following theorem is given: Theorem 3.9. Let \(C\) be a Cohen-Macaulay semi-dualizing complex for \(R\) and \(\mathbf y = y_1, \dots,y_n\) a sequence of elements in \({\mathfrak m}\). Suppose \(X\) is \(C\)-reflexive. Then \(\mathbf y\) is an \(X\)-parameter sequence if and only if it is an \(R\Hom_R(X,C)\)-sequence.

Keywords

Dimension theory, depth, related commutative rings (catenary, etc.), \(Y\)-sequence, Cohen-Macaulay defect, Complexes, Special types (Cohen-Macaulay, Gorenstein, Buchsbaum, etc.), bounded complex, anchor prime ideal

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
5
Average
Average
Average
bronze