Let $A$ be a finite dimensional $k$-algebra with 1. Denote by $_AP$ the category of projective left $A$-modules finite dimensional. And with $_AI$ the category of injective left $A$-modules finite dimensional. Denote by $D$ the duality with respect to $k$, i.e. $D(M)=\mathrm{Hom}_k(M,k)$. Then the following functor is a functor from $_AP$ to $_AI$:
$\nu=D\mathrm{Hom}_A(\;.\;,_AA)$
how can I prove it?
Define also
$\nu^{-1}=\mathrm{Hom}_A(D(A_A),\;.\;)$
how can I prove that this functor goes from $_AI$ into $_AP$?
I want to prove that $\nu$ and $\nu^{-1}$ are quasi-inverse, how can I do it?
Here they say there is an invertible natural transformation $\alpha_P:D\mathrm{Hom}(P,\;.\;)\rightarrow\mathrm{Hom}(\;.\;,\nu P)$ but I don't understand why it exists, why it is invertible and why this implies $\nu$ and $\nu^{-1}$ are quasi-inverse. Any help?