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@article{DE_1977_13_1_a16, author = {V. I. Pa\v{s}kovskii}, title = {Connected partial differential operators with different principal parts}, journal = {Differencialʹnye uravneni\^a}, pages = {121--125}, publisher = {mathdoc}, volume = {13}, number = {1}, year = {1977}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1977_13_1_a16/} }
V. I. Paškovskii. Connected partial differential operators with different principal parts. Differencialʹnye uravneniâ, Tome 13 (1977) no. 1, pp. 121-125. http://geodesic.mathdoc.fr/item/DE_1977_13_1_a16/