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- Category_of_abelian_groups abstract "In mathematics, the category Ab has the abelian groups as objects and group homomorphisms as morphisms. This is the prototype of an abelian category: indeed, every small abelian category can be embedded in Ab.The monomorphisms in Ab are the injective group homomorphisms, the epimorphisms are the surjective group homomorphisms, and the isomorphisms are the bijective group homomorphisms.The zero object of Ab is the trivial group {0} which consists only of its neutral element.Note that Ab is a full subcategory of Grp, the category of all groups. The main difference between Ab and Grp is that the sum of two homomorphisms f and g between abelian groups is again a group homomorphism:(f+g)(x+y) = f(x+y) + g(x+y) = f(x) + f(y) + g(x) + g(y) = f(x) + g(x) + f(y) + g(y) = (f+g)(x) + (f+g)(y)The third equality requires the group to be abelian. This addition of morphism turns Ab into a preadditive category, and because the direct sum of finitely many abelian groups yields a biproduct, we indeed have an additive category.In Ab, the notion of kernel in the category theory sense coincides with kernel in the algebraic sense, i.e.: the kernel of the morphism f : A → B is the subgroup K of A defined by K = {x in A : f(x) = 0}, together with the inclusion homomorphism i : K → A. The same is true for cokernels: the cokernel of f is the quotient group C = B/f(A) together with the natural projection p : B → C. (Note a further crucial difference between Ab and Grp: in Grp it can happen that f(A) is not a normal subgroup of B, and that therefore the quotient group B/f(A) cannot be formed.) With these concrete descriptions of kernels and cokernels, it is quite easy to check that Ab is indeed an abelian category. The product in Ab is given by the product of groups, formed by taking the cartesian product of the underlying sets and performing the group operation componentwise. Because Ab has kernels, one can then show that Ab is a complete category. The coproduct in Ab is given by the direct sum; since Ab has cokernels, it follows that Ab is also cocomplete. Taking direct limits in Ab is an exact functor, which turns Ab into an abelian category.We have a forgetful functor Ab → Set which assigns to each abelian group the underlying set, and to each group homomorphism the underlying function. This functor is faithful, and therefore Ab is a concrete category. The forgetful functor has a left adjoint (which associates to a given set the free abelian group with that set as basis) but does not have a right adjoint.An object in Ab is injective if and only if it is divisible; it is projective if and only if it is a free abelian group. The category has a projective generator (Z) and an injective cogenerator (Q/Z). This implies that Ab is an example of a Grothendieck category.Given two abelian groups A and B, their tensor product A⊗B is defined; it is again an abelian group. With this notion of product, Ab is a symmetric monoidal category.Ab is not cartesian closed (and therefore also not a topos) since it lacks exponential objects.".
- Category_of_abelian_groups wikiPageID "454748".
- Category_of_abelian_groups wikiPageRevisionID "549820574".
- Category_of_abelian_groups hasPhotoCollection Category_of_abelian_groups.
- Category_of_abelian_groups subject Category:Category-theoretic_categories.
- Category_of_abelian_groups subject Category:Group_theory.
- Category_of_abelian_groups type Abstraction100002137.
- Category_of_abelian_groups type Category-theoreticCategories.
- Category_of_abelian_groups type Class107997703.
- Category_of_abelian_groups type Collection107951464.
- Category_of_abelian_groups type Group100031264.
- Category_of_abelian_groups comment "In mathematics, the category Ab has the abelian groups as objects and group homomorphisms as morphisms.".
- Category_of_abelian_groups label "Categoria de grupos abelianos".
- Category_of_abelian_groups label "Categorie van abelse groepen".
- Category_of_abelian_groups label "Category of abelian groups".
- Category_of_abelian_groups label "Categoría de grupos abelianos".
- Category_of_abelian_groups label "Catégorie des groupes abéliens".
- Category_of_abelian_groups label "Категория абелевых групп".
- Category_of_abelian_groups sameAs Categoría_de_grupos_abelianos.
- Category_of_abelian_groups sameAs Catégorie_des_groupes_abéliens.
- Category_of_abelian_groups sameAs Categorie_van_abelse_groepen.
- Category_of_abelian_groups sameAs Categoria_de_grupos_abelianos.
- Category_of_abelian_groups sameAs Q1956793.
- Category_of_abelian_groups sameAs Q1956793.
- Category_of_abelian_groups sameAs Category_of_abelian_groups.
- Category_of_abelian_groups wasDerivedFrom Category_of_abelian_groups?oldid=549820574.
- Category_of_abelian_groups isPrimaryTopicOf Category_of_abelian_groups.