linguistic:voice_change, structural:reformatting
Additivity

If C and D are preadditive categories and F : D → C is an additive functor with a right adjoint G : C → D, then G is also an additive functor and the hom-set bijections

are, in fact, isomorphisms of abelian groups. Dually, if G is additive with a left adjoint F, then F is also additive.

Moreover, if both C and D are additive categories (i.e. preadditive categories with all finite biproducts), then any pair of adjoint functors between them are automatically additive.