Column Invariants Over Cohen–Macaulay Local Rings

Abstract

We define some numerical invariants over Cohen–Macaulay local rings. These invariants are related to columns of the presenting matrices of maximal Cohen–Macaulay modules and syzygy modules without free summands. We study the relationship between these invariants, and the invariant col(A).

     

On the Countability of Noetherian Dimension of Modules

Abstract

It is shown that a module M has countable Noetherian dimension if and only if the lengths of ascending chains of submodules of M has a countable upper bound. This shows in particular that every submodule of a module with countable Noetherian dimension is countably generated. It is proved that modules with Noetherian dimension over locally Noetherian rings have countable Noetherian dimension. We also observe that ω^ω is a universal upper bound for the lengths of all chains in Artinian modules over commutative rings.     

A SURJECTIVE HOMOMORPHISM OF LOCAL COHOMOLOGY MODULES

Let R be a local ring and M a finitely generated generalized Cohen-Macaulay R-module such that dim _R M = dim _R M/αM + height_Mα a for all ideals α of R. Suppose that H_I ^j(M) ≠ 0 for an ideal I of R and an integer j > height_M I. We show that there exists an ideal J ? such that a. height_M J = j;

b. the natural homomorphism H_I ^j(M) → H_I ^j(M) is an isomorphism, for all i > j; and,

c. the natural homomorphism H_I ^j(M) → H_I ^j(M) is surjective.

By using this theorem, we obtain some results about Betti numbers, coassociated primes, and support of local cohomology modules.     

On finitely injective modules and locally pure-injective modules over Prüfer domains

Over Matlis valuation domains there exist finitely injective modules which are not direct sums of injective modules, as well as complete locally pure-injective modules which are not the completion of a direct sum of pure-injective modules. Over Prüfer domains which are either almost maximal, or -local Matlis, finitely injective torsion modules and complete torsion-free locally pure-injective modules correspond to each other under the Matlis equivalence. Almost maximal Prüfer domains are characterized by the property that every torsion-free complete module is locally pure-injective. It is derived that semi-Dedekind domains are Dedekind.

     

相对Hopf模和广义cleft扩张

本文研究了π-cleft扩张的余代数分解问题及对偶的η-cocleft扩张的代数分解问题.利用相对Hopf模结构定理,给出了一个条件,使得具有余代数结构的π-cleft扩张有较好的余代数分解形式.作为特例,可以重新得到Radford给出的具有投射的双代数的双积分解定理.     

相关Yetter-Drinfel'd Hopf代数上的相关Hopf模结构定理

主要证明了相关Yetter-Drinfel'd Hopf代数上的相关Hopf模结构定理,不仅推广了Yetter-Drinfel'd Hopf代数上的Hopf模结构定理,而且推广了相关Hopf模结构定理.同时,给出相关Yetter-Drinfel'd Hopf代数上的Maschke定理.     

Congruences and ideals on Boolean modules: a heterogeneous point of view

Definitions for heterogeneous congruences and heterogeneous ideals on a Boolean module $\mathcal {M}$ are given and the respective lattices $\mathrm{Cong}\mathcal {M}$ and $\mathrm{Ide}\mathcal {M}$ are presented. A characterization of the simple bijective Boolean modules is achieved differing from that given by Brink in a homogeneous approach. We construct the smallest and the greatest modular congruence having the same Boolean part. The same is established for modular ideals. The notions of kernel of a modular congruence and the congruence induced by a modular ideal are introduced to describe an isomorphism between $\mathrm{Cong}\mathcal {M}$ and $\mathrm{Ide}\mathcal {M}$. This isomorphism leads us to conclude that the class of the Boolean module is ideal determined.