R. Montgomery, A Tour of Subriemannnian Geometries, Their Geodesics, and Applications (Am. Math. Soc., Providence, R.I., 2002).
A. Agrachev, D. Barilari, and U. Boscain, A Comprehensive Introduction to Sub-Riemannian Geometry from Hamiltonian Viewpoint (Cambridge Univ. Press, Cambridge, 2019).
A. M. Vershik and V. Ya. Gershkovich, “Nonholonomic dynamical systems: Geometry of distributions and variational problems,” Advances in Science and Engineering: Modern Problems in Mathematics: Fundamental Directions (VINITI, Moscow, 1987), Vol. 16, pp. 5–85.
A. Agrachev, B. Bonnard, M. Chyba, and I. Kupka, ESAIM: Control Optim. Calculus Var. 2, 377–448 (1997).
V. N. Berestovskii and I. A. Zubareva, Sib. Math. J. 42 (4), 613–628 (2001).
U. Boscain and F. Rossi, SIAM J. Control Optim. 47, 1851–1878 (2008).
Yu. L. Sachkov, ESAIM Control Optim. Calculus Var. 17, 293–321 (2011).
Y. A. Butt, Yu. L. Sachkov, and A. I. Bhatti, J. Dyn. Control Syst. 23, 155–195 (2017).
A. A. Ardentov and Yu. L. Sachkov, Regular Chaotic Dyn. 22 (8), 909–936 (2017).
M. Goresky and R. MacPherson, Stratified Morse Theory (Springer-Verlag, Berlin, 1988).
A. Agrachev, Rend. Semin. Mat. Torino 56, 1–12 (1998).
A. Agrachev and A. Sarychev, ESAIM: Control Optim. Calculus Var. 4, 377–403 (1999).
B. Bonnard and E. Trélat, Ann. Fac. Sci. Toulouse 6е Ser. 10 (3), 405–491 (2001).