@article{SM_1979_35_6_a0,
     author = {A. A. Agrachev and R. V. Gamkrelidze},
     title = {The exponential representation of flows and the chronological calculus},
     journal = {Sbornik. Mathematics},
     pages = {727--785},
     year = {1979},
     volume = {35},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1979_35_6_a0/}
}