What os the meaning of a reverse Langlands transform
to which Drinfeld seems to refer?



My guess is that, traditionally, the Geometric Langlands program seems to be looking for a functor from D_{coh}(Loc,O)\to D_{coh}(^L Bun,D), that is, from the derived category on the space of local systems to the derived category of Dmodules on the space of bundles for the Langlands dual. So, by reverse Langlands transformation, he might be asking for a functor in the other direction, to try to establish the equivalence. 

