$\newcommand{\C}{\mathcal{C}}\newcommand{\D}{\mathcal{D}}\newcommand{\op}{\mathrm{op}}$I would like to define the notion of a self-dual category, which should mean a category isomorphic to its opposite in a natural way, and the notion a self-dual functor between such categories. For a category $\C$, I denote by $\C^\op$ its opposite category; for a functor $F \colon \C \to \D$ its opposite functor is $F^\op \colon \C^\op \to \D^\op$; for a natural transformation $\eta \colon F \Rightarrow G$ I denote $\eta^\op \colon G^\op \Rightarrow F^\op$ its opposite natural transformation. 


**Definition**. A self-dual category is a category $\C$, a functor $i\_\C \colon \C \to \C^\op$, and a natural isomorphism $$\epsilon\_\C \colon i\_\C^\op \circ i\_\C \Rightarrow \mathrm{id}\_\C.$$


I think this is the "correct" definition. (Not quite, see below.) An example would be for $\C$ the category of finite dimensional vector spaces over a field $k$, and $i\_\C = \mathrm{Hom}(-,k)$. We would now like to talk about functors being self-dual, which should mean that they commute with taking duals.


**Definition**. A self-dual functor $\C \to \D$ is a functor $F \colon \C \to \D$ and a natural isomorphism 
$$ \eta \colon i\_\D \circ F \Rightarrow F^\op \circ i\_\C $$
satisfying the following coherence condition: The diagram of natural isomorphisms


$$\begin{matrix} F \circ i\_\C^{\op} & \stackrel{\eta^{\op}}{\Rightarrow} & i\_\D^{\op} \circ F^{\op} \\\\ \epsilon\_D \Uparrow ~ ~ ~ & & ~ ~ ~ \Downarrow \epsilon\_C^{\op} \\\\ i\_\D^{\op} \circ i\_\D \circ F \circ i\_\C^{\op} & \stackrel{\eta}{\Rightarrow} & i\_\D^{\op} \circ F^{\op} \circ i\_\C \circ i\_\C^{\op} \end{matrix}$$


commutes.


This whole definition is quite a mouthful and it feels like someone ought to have defined this carefully somewhere. Googling for self-dual or autodual categories produces several hits where people use this term for categories isomorphic to their opposite, but I haven't seen anyone discuss categories which have such an isomorphism in a coherent way. Does anyone know whether there is such a reference? Maybe this is a special case of a more general construction?



What is a self-dual category?
The question has essentially been answered in the comments, I am recording this here so that the question does not get bumped back to the top. Theo Buehler and Buschi Sergio both gave nice references, and it seems that this notion is well known in K-theory under the name "category with duality". Martin's remarks were also helpful.


