@article{DE_1972_8_5_a6,
     author = {N. N. Ladis},
     title = {Energy functions for certain dynamical systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {790--794},
     publisher = {mathdoc},
     volume = {8},
     number = {5},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_5_a6/}
}