Abelian categories are the most general category in which one can The idea and the name “abelian category” were first introduced by. In mathematics, an abelian category is a category in which morphisms and objects can be .. Peter Freyd, Abelian Categories; ^ Handbook of categorical algebra, vol. 2, F. Borceux. Buchsbaum, D. A. (), “Exact categories and duality”. BOOK REVIEWS. Abelian categories. An introduction to the theory of functors. By Peter. Freyd. (Harper’s Series in Modern Mathematics.) Harper & Row.

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Important theorems that apply in all abelian categories include the five lemma and the short five lemma as a special caseas well as the snake lemma and fregd nine lemma as a special case. The last point is of relevance in particular for higher categorical generalizations of additive categories.

It is such that much of the homological algebra of chain complexes can be developed inside every abelian category.

## Abelian category

Proposition In an abelian category every morphism decomposes uniquely categoriess to a unique isomorphism into the composition of an epimorphism and a monomorphismvia prop combined with def. This result can be found as Theorem 7. Let C C be an abelian category. Abelian categories are very stable categories, for example they are regular and they satisfy the snake lemma. This highlights the foundational relevance of the category of Abelian groups in the theory and its canonical nature. See AT category for more on that.

Going still further one should be able to obtain a nice theorem describing the image of the embedding of the weak 2-category of. They are the following:. Remark Some references claim that this property characterizes abelian categories among pre-abelian ones, but it is not clear to the authors of this page why this should be so, although we do not currently have a counterexample; see this discussion.

Given any pair AB of objects in an abelian category, there is a special zero morphism from A to B. The motivating prototype example of an abelian category is the category of abelian groupsAb.

Let A be an abelian category, C a full, additive subcategory, and I the inclusion functor. The proof that R Mod R Mod is an abelian category is spelled out for categorues in.

### Abelian Categories

All of the constructions used in that field are relevant, such as exact sequences, and especially short exact sequencesand derived functors. Definition An abelian category is a pre-abelian category satisfying the following equivalent conditions. There are numerous types of full, additive subcategories of abelian categories that occur in nature, as well as some conflicting terminology. A similar statement is true for additive categoriesalthough the most natural result in that case gives only enrichment over abelian monoids categoriee see semiadditive category.

Theorem Let C C be an abelian category. While additive categories differ significantly from toposesthere is an intimate relation between abelian categories abellan toposes.

From Wikipedia, the free encyclopedia. This definition is equivalent [1] to the wbelian “piecemeal” definition:. Axioms AB1 and AB2 were also given.

Subobjects and quotient objects are well-behaved in abelian categories. They are what make an additive category abelian. Therefore in particular the category Vect of vector spaces is an abelian category. The concept of exact sequence arises naturally in this setting, and it turns out that exact functorsi.

### abelian category in nLab

This can be defined as the zero element of the hom-set Hom ABsince this is an abelian group. An abelian category is a pre-abelian category satisfying the following equivalent conditions. The Ab Ab -enrichment of an abelian category need not be specified a priori. In an abelian category, every morphism f can be written as the composition of aelian epimorphism followed by fategories monomorphism.

Every abelian category A is a module over the monoidal category of finitely generated abelian groups; that is, we can form a tensor product of a finitely generated abelian group G and any object A of A. Abelian categories are named after Niels Henrik Abel. However, in most examples, the Ab Ab -enrichment is evident from the start and does abeliaj need to be constructed in this way. Some references claim that this property characterizes abelian categories among pre-abelian ones, but it is not clear to the authors of this page why this should be so, although we do not currently have a counterexample; see this discussion.

Every small abelian category admits a fullfaithful and cagegories functor to the category R Mod R Mod for some ring R R.

## Abelian categories

Proof This result can be found as Theorem 7. The two were defined differently, but they had similar properties. Proposition These two conditions are indeed equivalent. Retrieved from ” https: Here is an explicit example of a full, additive subcategory of an abelian category which is itself abelian but the inclusion functor is not exact. Views Read Edit View history. But under suitable conditions this comes down to working subject to an embedding into Ab Absee the discussion at Embedding into Ab below.

Every monomorphism is a kernel and every epimorphism categoriies a cokernel. If an arbitrary not necessarily pre-additive locally small category C C has a zero objectbinary products and coproducts, kernels, cokernels and the property that every monic is a kernel arrow and every epi is a cokernel arrow so that all monos and epis are normalthen it can be equipped with a unique addition on the morphism sets such that composition is bilinear and C C is abelian categoriex respect to this structure.

Remark By the second formulation of the definitionin an abelian category every monomorphism is a regular monomorphism ; every epimorphism is a regular epimorphism.