@article{MS2_1961__9_165779,
     author = {Jaak Peetre},
     title = {On {Estimating} the {Solutions} of {Hypoelliptic} {Differential} {Equations} {Near} the {Plane} {Boundary.}},
     journal = {Mathematica Scandinavica},
     pages = {337--351},
     publisher = {mathdoc},
     volume = {9},
     year = {1961},
     zbl = {0113.30601},
     url = {http://geodesic.mathdoc.fr/item/MS2_1961__9_165779/}
}