$(n,d)$-Coherent Rings

TL;DR

This paper explores generalized coherence conditions on rings related to modules with bounded projective dimension, providing new characterizations of $(n,d)$-coherent rings and their connections to existing notions.

Contribution

It develops a relative homological framework for $(n,d)$-coherent rings, extending previous concepts and offering new characterizations in terms of finitely presented modules.

Findings

Characterizations of left $(n,d)$-coherent rings via classes of finitely $n$-presented modules

Connections between $(n,d)$-coherence and Costa's $n$-coherence

New descriptions of regularly coherent rings

Abstract

We investigate finiteness conditions on modules of bounded projective dimension and their connection with generalized notions of coherence. For a ring $R$, we consider the class $\mathsf{FP}_n^{\le d}(R)$ of finitely $n$-presented modules of projective dimension at most $d$ and develop the corresponding relative homological theory. We establish several characterizations of left $(n,d)$-coherent rings in the sense of Mao and Ding [43], in terms of $\mathsf{FP}_n^{\le d}(R)$ and the associated classes of $\mathsf{FP}_n^{\le d}$-injective, $\mathsf{FP}_n^{\le d}$-projective, $\mathsf{FP}_n^{\le d}$-flat, and $\mathsf{FP}_n^{\le d}$-cotorsion modules. As a consequence, when $d \ge \gD(R)$ or $d=\infty$, we recover Costa's $n$-coherence [17] and obtain new characterizations of regularly coherent rings.