More on the Concept of Duality in Convex Analysis, the Characterizations of Fenchel Transform and Identity

In this paper, with a different approach, we first show that for a Banach space $X$ there is a fully order reversing mapping $T$ from ${\rm conv}(X)$ (the cone of all extended real-valued lower semicontinuous proper convex functions defined on $X$) to itself if and only if $X$ is reflexive and linearly isomorphic to its dual $X^*$ (hence, resolve an open question). We then show the the Artstein-Avidan-Milman representation theorem holds: For every fully order reversing mapping $T:{\rm conv}(X)\rightarrow {\rm conv}(X)$ there exists a linear isomorphism $U:X\rightarrow X^*$, $x_0^*, \;\varphi_0\in X^*$, $\alpha>0$ and $r_0\in\mathbb R$ so that \begin{equation}\nonumber (Tf)(x)=\alpha(\mathcal Ff)(Ux+x^*_0)+\langle\varphi_0,x\rangle+r_0,\;\;\forall x\in X, \end{equation} where $\mathcal F: {\rm conv}(X)\rightarrow {\rm conv}(X^*)$ is the Fenchel transform. We also show several representation theorems of fully order preserving mappings defined on certain cones of convex functions. For example, for every fully order preserving mapping $S:{\rm semn}(X)\rightarrow {\rm semn}(X)$ there is a linear isomorphism $U:X\rightarrow X$ so that \begin{equation}\nonumber (Sf)(x)=f(Ux),\;\;\forall f\in{\rm semn}(X),\;x\in X, \end{equation} where ${\rm semn}(X)$ is the cone of all lower semicontinuous seminorms on $X$.