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@article{MAT_1971_15_4_a2, author = {L. Nirenberg and F. Tr\`eves}, title = {On local solvability of linear partial differential equations. {II.~Sufficient} conditions}, journal = {Matematika}, pages = {68--110}, publisher = {mathdoc}, volume = {15}, number = {4}, year = {1971}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MAT_1971_15_4_a2/} }
L. Nirenberg; F. Trèves. On local solvability of linear partial differential equations. II.~Sufficient conditions. Matematika, Tome 15 (1971) no. 4, pp. 68-110. http://geodesic.mathdoc.fr/item/MAT_1971_15_4_a2/