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@article{FAA_1979_13_1_a1, author = {I. M. Gel'fand and L. A. Dikii}, title = {Integrable nonlinear equations and the {Liouville} theorem}, journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a}, pages = {8--20}, publisher = {mathdoc}, volume = {13}, number = {1}, year = {1979}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/FAA_1979_13_1_a1/} }
I. M. Gel'fand; L. A. Dikii. Integrable nonlinear equations and the Liouville theorem. Funkcionalʹnyj analiz i ego priloženiâ, Tome 13 (1979) no. 1, pp. 8-20. http://geodesic.mathdoc.fr/item/FAA_1979_13_1_a1/