@article{SM_1992_72_1_a1,
     author = {A. A. Agrachev and R. V. Gamkrelidze},
     title = {Symplectic geometry and conditions necessary conditions for optimality},
     journal = {Sbornik. Mathematics},
     pages = {29--45},
     publisher = {mathdoc},
     volume = {72},
     number = {1},
     year = {1992},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1992_72_1_a1/}
}