Minimal Lagrangian diffeomorphisms between domains in the hyperbolic   plane
  Let N be a complete, simply-connected surface of constant curvature \kappa \leq 0. Moreover, suppose that \Omega and \tilde{\Omega} are strictly convex domains in N with the same area. We show that there exists an area-preserving diffeomorphism from \Omega to \tilde{\Omega} whose graph is a minimal submanifold of N \times N. 
S. Brendle