@article{COCV_1997__2__377_0,
     author = {Agrachev, A. and Bonnard, B. and Chyba, M. and Kupka, I.},
     title = {Sub-riemannian sphere in {Martinet} flat case},
     journal = {ESAIM: Control, Optimisation and Calculus of Variations},
     pages = {377--448},
     publisher = {EDP-Sciences},
     volume = {2},
     year = {1997},
     mrnumber = {1483765},
     zbl = {0902.53033},
     language = {en},
     url = {http://www.numdam.org/item/COCV_1997__2__377_0/}
}