@article{ASNSP_1968_3_22_3_409_0,
     author = {Arkeryd, Leif},
     title = {A priori estimates for hypoelliptic differential equations in a half-space},
     journal = {Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche},
     pages = {409--424},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 22},
     number = {3},
     year = {1968},
     mrnumber = {236518},
     zbl = {0162.41002},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1968_3_22_3_409_0/}
}