On Pro-zero homomorphisms and sequences in local (co-)homology

TL;DR

This paper explores conditions under which sequences are pro-regular or weakly pro-regular in local (co-)homology, extending previous work to non-Noetherian rings and applying these concepts to prisms in algebraic geometry.

Contribution

It generalizes the notions of pro-regularity using Čech (co-)homology, extending the theory to non-Noetherian rings and connecting to recent developments in prismatic cohomology.

Findings

Characterization of pro-regularity via Čech cohomology and homology.

Extension of pro-regularity concepts to non-Noetherian rings.

Application to prismatic structures in algebraic geometry.

Abstract

Let $\xx= x_1,\ldots,x_r$ denote a system of elements of a commutative ring $R$. For an $R$-module $M$ we investigate when $\xx$ is $M$-pro-regular resp. $M$-weakly pro-regular as generalizations of $M$-regular sequences. This is done in terms of \v{C}ech co-homology resp. homology, defined by $H^i(\check{C}_{\xx} \otimes_R \cdot)$ resp. by $H_i({\textrm{R}} \Hom_R(\check{C}_{\xx},\cdot)) \cong H_i(\Hom_R(\mathcal{L}_{\xx},\cdot))$, where $\check{C}_{\xx}$ denotes the \v{C}ech complex and $\mathcal{L}_{\xx}$ is a bounded free resolution of it as constructed in [17] resp. [16]. The property of $\xx$ being $M$-pro-regular resp. $M$-weakly pro-regular follows by the vanishing of certain \v{C}ech co-homology resp. homology modules, which is related to completions. This extends previously work by Greenlees and May (see) [5] and Lipman et al. (see [1]}). This contributes to a further understanding of \v{C}ech (co-)homology in the non-Noetherian case. As a technical tool we use one of Emmanouil's results (see [4]) about the inverse limits and its derived functor. As an application we prove a global variant of the results with an application to prisms in the sense of Bhatt and Scholze (see[3]).