@article{MAN_1984__269_163927,
     author = {Toshinori Oaku},
     title = {Analytic {Hypo-Ellipticity} and {Propagation} of {Regularity} for a {System} of {Microdifferential} {Equations} with {Non-Involutory} {Characteristics.}},
     journal = {Mathematische Annalen},
     pages = {145--168},
     publisher = {mathdoc},
     volume = {269},
     year = {1984},
     zbl = {0535.35012},
     url = {http://geodesic.mathdoc.fr/item/MAN_1984__269_163927/}
}