@article{MZ_1996__223_3_174919,
     author = {A.P. Bergamasco and P.D. Cordaro and G. Petronilho},
     title = {Global solvability for certain classes of underdetermined systems of vector fields.},
     journal = {Mathematische Zeitschrift},
     pages = {261--274},
     publisher = {mathdoc},
     volume = {223},
     number = {3},
     year = {1996},
     zbl = {0863.58062},
     url = {http://geodesic.mathdoc.fr/item/MZ_1996__223_3_174919/}
}