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@article{MAT_1968_12_2_a3, author = {L. V. H\"ormander}, title = {Hypoelliptic differential equations of second order}, journal = {Matematika}, pages = {88--109}, publisher = {mathdoc}, volume = {12}, number = {2}, year = {1968}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MAT_1968_12_2_a3/} }
L. V. Hörmander. Hypoelliptic differential equations of second order. Matematika, Tome 12 (1968) no. 2, pp. 88-109. http://geodesic.mathdoc.fr/item/MAT_1968_12_2_a3/