@article{MAN_1985__272_164008,
     author = {Michael Langenbruch},
     title = {On the {Functional} {Dimension} of {Solution} {Spaces} of {Hypoelliptic} {Partial} {Differential} {Operators.}},
     journal = {Mathematische Annalen},
     pages = {217--230},
     publisher = {mathdoc},
     volume = {272},
     year = {1985},
     zbl = {0556.35028},
     url = {http://geodesic.mathdoc.fr/item/MAN_1985__272_164008/}
}