@article{article1c0b271b,
title   = {Globally analytic hypoelliptic vector fields on compact surfaces},
author = {Bergamasco, Adalberto Panobianco and Zani, Sérgio Luís},
year = {2008},
doi = {10.1090/s0002-9939-07-09097-1},
journal   = {Proceedings of the American Mathematical Society}
}