1. Agrachev, A.A., Sachkov, Y.L.: Control theory from the geometric viewpoint, Encyclopaedia of Mathematical Sciences, vol. 87. Springer-Verlag, Berlin (2004). Control Theory and Optimization, II
2. Amano, K.: Maximum principles for degenerate elliptic-parabolic operators. Indiana Univ. Math. J. 28(4), 545–557 (1979)
3. Bauer, H.: Harmonische Räume und ihre Potentialtheorie. Ausarbeitung einer im Sommersemester 1965 an der Universität Hamburg gehaltenen Vorlesung. Lecture Notes in Mathematics, No. 22. Springer-Verlag, Berlin-New York (1966)
4. Bonfiglioli, A., Lanconelli, E.: Matrix-exponential groups and Kolmogorov-Fokker-Planck equations. J. Evol. Equ. 12(1), 59–82 (2012)
5. Bonfiglioli, A., Lanconelli, E., Uguzzoni, F.: Uniform Gaussian estimates for the fundamental solutions for heat operators on Carnot groups. Adv. Differ. Equ. 7 (10), 1153–1192 (2002)