The normal decomposition of a morphism in categories without zeros

TL;DR

This paper introduces a new elementary method for decomposing morphisms in categories without zeros, generalizing the standard normal decomposition to non-pointed categories and exploring their properties.

Contribution

It provides a novel construction of normal decompositions in non-pointed categories, extending classical concepts and analyzing their behavior and applications.

Findings

Normal decompositions can be constructed in categories without zeros.

The generalized notions of normal monomorphisms and epimorphisms are introduced.

Applications are illustrated in categories like T1-spaces and groups.

Abstract

For a morphism f in a category C with sufficiently many finite limits and colimits, we discuss an elementary construction of a decomposition of f through objects P and N which, if C happens to have a zero object, amounts to the standard decomposition of f through P = Coker(ker f) and N = Ker(coker f). In this way we obtain natural notions of normal monomorphism and normal epimorphism also in non-pointed categories, as special types of regular mono- and epimorphisms. We examine the factorization behaviour of these classes of morphisms in general, compare the generalized normal decompositions with other types of threefold factorizations, and illustrate them in some every-day categories. The concrete construction of normal decompositions in the slices or coslices of these categories can be challenging. Amongst many others, in this regard, we consider particularly the categories of T1-spaces and of groups.