@article{articlee7769c3b,
title   = {Global s-solvability and global s-hypoellipticity for certain perturbations of zero order of systems of constant real vector fields},
author = {Petronilho, G and Zani, Sérgio Luís},
year = {2008},
doi = {10.1016/j.jde.2008.02.020},
journal   = {Journal of Differential Equations}
}