@article{DE_1977_13_5_a0,
     author = {L. A. Cherkas},
     title = {Methods for estimating the number of limit cycles of autonomous systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {779--802},
     publisher = {mathdoc},
     volume = {13},
     number = {5},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_5_a0/}
}