Abelian Categories
Additive and abelian categories, the axioms, exactness in a general abelian category, the Freyd-Mitchell embedding theorem, and the standard examples.
Every page in the KEVOS library tagged Categories & Functors. 8 pages.
Additive and abelian categories, the axioms, exactness in a general abelian category, the Freyd-Mitchell embedding theorem, and the standard examples.
Adjoint pairs, unit and counit, the tensor-hom adjunction, preservation of limits and colimits, and the exactness consequences that make adjointness central to homological algebra.
Categories, objects and morphisms, monomorphisms and epimorphisms defined by cancellation, isomorphisms, and why the arrow-theoretic definitions differ from the element-based ones.
The opposite category, the duality principle, dual pairs of notions in homological algebra, and the limits of formal duality.
Covariant and contravariant functors, composition, additive functors, faithful and full functors, and the exactness hierarchy that governs derived functors.
Natural transformations and naturality squares, natural isomorphisms, functor categories, and the role of naturality in the long exact sequences.
Universal properties, products and coproducts in a general category, initial and terminal objects, and uniqueness up to unique isomorphism.
Pullbacks and pushouts, their construction in module categories, limits and colimits over a diagram, and exactness of filtered colimits.