@article{DE_1969_5_9_a1,
     author = {V. V. Nemytskii and Yu. V. Malyshev},
     title = {A qualitative investigation of potential systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1550--1557},
     publisher = {mathdoc},
     volume = {5},
     number = {9},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1969_5_9_a1/}
}