@article{GDZPPN002350343, title = {Partial Hypoellipticity and Gevrey Classes.}, journal = {Mathematica Scandinavica}, volume = {27}, year = {1970}, pages = {119-131}, zbl = {0201.12502}, url = {http://dml.mathdoc.fr/item/GDZPPN002350343} }
Claesson, Tomas. Partial Hypoellipticity and Gevrey Classes.. Mathematica Scandinavica, Tome 27 (1970) pp. 119-131. http://gdmltest.u-ga.fr/item/GDZPPN002350343/