@article{TM_1998_220_a1,
     author = {A. A. Agrachev and P. Zezza and G. Stefani},
     title = {Strong minima in optimal control},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {8--26},
     year = {1998},
     volume = {220},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1998_220_a1/}
}