3 citations to https://www.mathnet.ru/eng/dan8940

1. E. R. Avakov, A. V. Arutyunov, D. Yu. Karamzin, “An investigation of smooth maps in a neighbourhood of an abnormal point”, Izv. Math., 78:2 (2014), 213–250                
2. A. A. Agrachev, R. V. Gamkrelidze, “Symplectic geometry and conditions necessary conditions for optimality”, Math. USSR-Sb., 72:1 (1992), 29–45            
3. A. A. Agrachev, “One more condition for a conditional extremum”, Russian Math. Surveys, 44:5 (1989), 189–190