# Bulletin of theKorean Mathematical SocietyBKMS

ISSN(Print) 1015-8634 ISSN(Online) 2234-3016

## Article

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Bull. Korean Math. Soc. 2021; 58(6): 1387-1400

Published online November 30, 2021 https://doi.org/10.4134/BKMS.b200924

## Admissible balanced pairs over formal triangular matrix rings

Lixin Mao

Nanjing Institute of Technology

### Abstract

Suppose that $T=\left(\begin{smallmatrix} A&0\\U&B \end{smallmatrix}\right)$ is a formal triangular matrix ring, where $A$ and $B$ are rings and $U$ is a $(B, A)$-bimodule. Let $\mathfrak{C}_{1}$ and $\mathfrak{C}_{2}$ be two classes of left $A$-modules, $\mathfrak{D}_{1}$ and $\mathfrak{D}_{2}$ be two classes of left $B$-modules. We prove that $(\mathfrak{C}_{1},\mathfrak{C}_{2})$ and $(\mathfrak{D}_{1},\mathfrak{D}_{2})$ are admissible balanced pairs if and only if $(\textbf{p}(\mathfrak{C}_{1}, \mathfrak{D}_{1}), \textbf{h}(\mathfrak{C}_{2}, \mathfrak{D}_{2}))$ is an admissible balanced pair in $T$-Mod. Furthermore, we describe when $(\mathfrak{P}^{\mathfrak{C}_{1}}_{\mathfrak{D}_{1}}, \mathfrak{I}^{\mathfrak{C}_{2}}_{\mathfrak{D}_{2}})$ is an admissible balanced pair in $T$-Mod. As a consequence, we characterize when $T$ is a left virtually Gorenstein ring.

Keywords: Formal triangular matrix ring, balanced pair, cotorsion pair

MSC numbers: Primary 16D20, 16D90, 16E05

Supported by: This work was financially supported by NSFC (11771202).