# Pretorsion theories in general categories

## TL;DR

This paper introduces pretorsion theories in general categories, extending classical torsion theories, and explores their properties and examples in categories like endomappings of finite sets and preordered sets.

## Contribution

It develops the concept of pretorsion theories in arbitrary categories, generalizing classical torsion theories, and provides new examples and foundational properties.

## Key findings

- Defines pretorsion theories in general categories.
- Establishes properties and structure of pretorsion theories.
- Provides new examples in specific categories such as endomappings and preordered sets.

## Abstract

We present a setting for the study of torsion theories in general categories. The idea is to associate, with any pair ($\mathcal T$, $\mathcal F$) of full replete subcategories in a category $\mathcal C$, the corresponding full subcategory $\mathcal Z = \mathcal T \cap \mathcal F$ of \emph{trivial objects} in $\mathcal C$. The morphisms which factor through $\mathcal Z$ are called $\mathcal Z$-trivial, and these form an ideal of morphisms, with respect to which one can define $\mathcal Z$-prekernels, $\mathcal Z$-precokernels, and short $\mathcal Z$-preexact sequences. This naturally leads to the notion of pretorsion theory, which is the object of study of this article, and includes the classical one in the abelian context when $\mathcal Z$ is reduced to the $0$-object of $\mathcal C$. We study the basic properties of pretorsion theories, and examine some new examples in the category of all endomappings of finite sets and in the category of preordered sets.

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Source: https://tomesphere.com/paper/1908.03546