@article{FAA_1980_14_1_a10,
     author = {V. E. Zakharov and A. V. Mikhailov},
     title = {Variational principle for equations integrable by the inverse problem method},
     journal = {Funkcionalʹnyj analiz i ego prilo\v{z}eni\^a},
     pages = {55--56},
     publisher = {mathdoc},
     volume = {14},
     number = {1},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/FAA_1980_14_1_a10/}
}