Definition:Acyclic Resolution
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Definition
Let $\mathbf A$ be an abelian category with enough injectives.
Let $\mathbf B$ be an arbitrary abelian category.
Let $F : \mathbf A \to \mathbf B$ be a left-exact functor.
Let $X$ be an object in $\mathbf A$.
An $F$-acyclic resolution of $X$ is a cochain complex $P := \family {d^i : I^i \to I^{i + 1} }_{i \mathop \in \Z}$ in $\mathbf A$, such that:
- $(1): \quad \forall i < 0 : I^i = 0$
- $(2): \quad I^i$ is $F$-acyclic for all $i \ge 0$
together with a morphism $\varepsilon : X \to I^0$, such that the cochain complex:
- $\begin{xy}
\xymatrix{ \dots \ar[r] & 0 \ar[r] & 0 \ar[r] & X \ar[r]^{\varepsilon} & I^0 \ar[r]^{d^0} & I^1 \ar[r]^{d^1} & I^2 \ar[r]^{d^2} & \dots } \end{xy}$ is exact.