additive functor
1. Definition
An additive functor is an Ab-enriched functor
2. Explicite
Let \(\mathcal{A}, \mathcal{B}\) be preadditive (?) categories and \(F: \mathcal{C} \rightarrow \mathcal{D}\) a functor. Then \(F\) is said to be additive, if for \(A,B \in \mathrm{Ob}(\mathcal{A})\)
\begin{align*} F: \mathrm{Hom}_{\mathcal{A}}(A,B) \rightarrow \mathrm{Hom}_{\mathcal{A}}(F(A), F(B)) \end{align*}is a group homomorphism
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