@article{DE_1984_20_12_a3,
     author = {G. S. Krechetov},
     title = {Lyapunov functions for second-order autonomous systems of classes $5${\textendash}$7$},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2048--2053},
     year = {1984},
     volume = {20},
     number = {12},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1984_20_12_a3/}
}