@incollection{AST_1981__89-90__117_0,
     author = {Abramczuk, W.},
     title = {A remark on ellipticity of systems of linear partial differential equations with constant coefficients},
     booktitle = {Analytic solutions of partial differential equations - Trento, 1981},
     series = {Ast\'erisque},
     pages = {117--128},
     publisher = {Soci\'et\'e math\'ematique de France},
     number = {89-90},
     year = {1981},
     mrnumber = {666405},
     zbl = {0532.35008},
     language = {en},
     url = {http://archive.numdam.org/item/AST_1981__89-90__117_0/}
}