Strong-weak coupling dualities in 2-dimensional quantum theory
possess a long history, with a remarkable range of applications.
Target space dualities between non-linear sigma model, for example,
often allow to sum up contributions from world-sheet instantons, a
task that would seem virtually impossible without duality symmetries. In recent years, a new class of curved target spaces has come
into focus through the AdS/CFT correspondence. As simple examples
show, the corresponding sigma model theories receive non-perturbative alpha' corrections. It would be of obvious interest to capture
those through perturbative expansions in some dual world-sheet
theory, whenever such a dual exists. In my talk I will explain
and derive a prototypical example for a weakly coupled string
dual of a strongly coupled holographic background.
