1. A. A. Agrachev, Quadratic mappings in geometric control theory. (Russian)Itogi Nauki i Tekhniki; Problemy Geometrii, VINITI, Akad. Nauk SSSR, Vol. 20Moscow, 1988, 11–205. English translation:J. Sov. Math. 51 (1990), 2667–2734.
2. A. A. Agrachev and R.V. Gamkrelidze, Second-order optimality condition for the time-optimal problem. (Russian)Mat. Sb. 100 (1976), 610–643. English translation:Math. USSR Sb. 29 (1976), 547–576.
3. —, Exponential representation of flows and chronological calculus. (Russian)Mat. Sb. 107 (1978), 467–532. English translation:Math. USSR Sb.,35 (1979), 727–785.
4. A. A. Agrachev, R. V. Gamkrelidze, and A. V. Sarychev, Local invariants of smooth control systems.Acta Appl. Math. 14 (1989), 191–237.
5. A. A. Agrachev and A. V. Sarychev On abnormal extremals for lagrange variational problems.J. Math. Syst., Estimation and Control (to appear).