@incollection{AST_1981__89-90__249_0,
     author = {Rodino, L.},
     title = {Gevrey hypoellipticity for a class of operators with multiple characteristics},
     booktitle = {Analytic solutions of partial differential equations - Trento, 1981},
     series = {Ast\'erisque},
     pages = {249--262},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {89-90},
     year = {1981},
     mrnumber = {666412},
     zbl = {0501.35021},
     language = {en},
     url = {http://www.numdam.org/item/AST_1981__89-90__249_0/}
}