@article{DE_2003_39_10_a4,
     author = {L. A. Cherkas},
     title = {An {Estimate} of the {Number} of {Limit} {Cycles} via {Critical} {Points} of {Conditional} {Extremum}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1334--1342},
     publisher = {mathdoc},
     volume = {39},
     number = {10},
     year = {2003},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2003_39_10_a4/}
}