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@article{MZ_1968__106_171012, author = {Johann Walter}, title = {Symmetrie elliptischer {Differentialoperatoren.}}, journal = {Mathematische Zeitschrift}, pages = {149--152}, publisher = {mathdoc}, volume = {106}, year = {1968}, zbl = {0159.40202}, url = {http://geodesic.mathdoc.fr/item/MZ_1968__106_171012/} }
Johann Walter. Symmetrie elliptischer Differentialoperatoren.. Mathematische Zeitschrift, Tome 106 (1968), pp. 149-152. http://geodesic.mathdoc.fr/item/MZ_1968__106_171012/