On Self-dual Gravity Structures on Ground Ring Manifolds in   Two-Dimensional String Theory
  We generalize the geometric structures generated by Witten's ground ring. It is shown that these generalized structures involve in a natural way some geometric constructions from Self-dual gravity [1,12]. The formal twistor construction on full quantum ground ring manifold is also given. 
H. Garcia-Compean, J.F. Plebanski, M. Przanowski