@article{oai:tsukuba.repo.nii.ac.jp:00017222,
 author = {Morioka, Tatsushi},
 issue = {3},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {739--762},
 title = {Hypoellipticite pour un certain operateur a caracteristique double},
 volume = {21},
 year = {1997}
}