@article{ASNSP_1981_4_8_4_575_0,
     author = {Mascarello Rodino, Maria and Rodino, Luigi},
     title = {A class of pseudo differential operators with multiple non-involutive characteristics},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {575--603},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 8},
     number = {4},
     year = {1981},
     mrnumber = {656001},
     zbl = {0441.35069},
     language = {en},
     url = {http://archive.numdam.org/item/ASNSP_1981_4_8_4_575_0/}
}