[1]  Cinti C,  Pascucci A,  Polidoro S. Pointwise estimates for solutions to a class of non-homogenous Kolmogorov equations. Mathematische Annalen,  2008, 340(2):  237--264

[2]  Cinti C,  Polidoro S.  Pointwise local estimates and Gaussian upper bounds for a class of uniformly subelliptic ultraparabolic operators.  J Math Anal Appl, 2008, 338:  946--969

[3]  Folland G B.  Subellitic estimates and function space on nilpotent Lie groups.  Ark Math, 1975, 13(2): 161--207

[4]  Gilberg D,  Trudinger N  S. Elliptic Partial Differential Equations of Second Order.  3nd ed,  Berlin: Springer-Verlag, 2001

[5]  Lanconelli E, Polidoro S.  On a class of hypoelliptic evolution operaters.  Rend Sem Mat Univ Politec Torino, 1994, 52(1):  29--63

[6]  Pascucci A,  Polidoro  S.  The moser's iterative method for a class of ultraparabolic equations.  Commun Contemp Math,  2004, 6(3):  395--417

[7]  Wang W, Zhang L.  The C^α regularity of a class of non-homogeneous ultraparabolic equations. http://arxiv. org/arXiv:math.AP/0711. 3411

[8]  Wang W, Zhang L. The C^α regularity of a class of hypoelliptic ultraparabolic equations.  http://arxiv.org/ arXiv: math. AP/0804. 4358v2

[9]  Weber M. The fundamental solution of a degenerate partial differential equation of parabolic type.  Trans Amer Math Soc, 1951, 71: 24--37

[10]  Zhang L. The C^α reglarity of a class of ultraparabolic equations. http://arxiv.org/arXiv:math.AP/ 0510405v2

[11]  Zhang L.  The C^α reglarity of a class of ultraparabolic equations.   Studies in Adv Math, Vol 42. AMS/IP, 2008:  619--622
 

[12]  Xin Z P, Zhang L, Zhao J N. Global well-posedness for the two dimensional Prandtl's boundary layer equation.