@article{article77b691ac,
title   = {Global solvability for certain classes of underdetermined systems of vector fields},
author = {Bergamasco, Adalberto Panobianco and Cordaro, Paulo Domingos and Petronilho, Gerson},
year = {1996},
doi = {10.1007/pl00004558},
journal   = {Mathematische Zeitschrift}
}