Lipschitz continuity and convexity preserving for solutions of   semilinear evolution equations in the Heisenberg group
  In this paper we study viscosity solutions of semilinear parabolic equations in the Heisenberg group. We show uniqueness of viscosity solutions with exponential growth at space infinity. We also study Lipschitz and horizontal convexity preserving properties under appropriate assumptions. Counterexamples show that in general such properties that are well-known for semilinear and fully nonlinear parabolic equations in the Euclidean spaces do not hold in the Heisenberg group. 
Qing Liu, Juan Manfredi, Xiaodan Zhou
math.AP