A wide class of examples of pretorsion theories and related remarks

Abstract

In this paper we construct a wide class of examples of \emph{pretorsion theories} in the sense of A. Facchini, C. Finocchiaro, and M. Gran. Given a category $\mathbb{C}$ with a terminal object $1$ and a category $\mathbb{D}$ with an initial object $0$, we show that $(\mathbb{C}\times \mathbf{0},\mathbf{1}\times\mathbb{D})$ is a pretorsion theory in $\mathbb{C}\times\mathbb{D}$ if and only if each morphism $0\to C$ in $\mathbb{C}$ is a monomorphism, and each morphism $D\to 1$ in $\mathbb{D}$ is an epimorphism. Here $\mathbf{0}$ denotes the set of initial objects in $\mathbb{D}$ and $\mathbf{1}$ denotes the set of terminal objects in $\mathbb{C}$. We then remark that the result generalised to products of arbitrary pretorsion theories.