@article{DE_2006_42_2_a8,
     author = {L. A. Cherkas and A. A. Grin'},
     title = {Spline approximations in the problem of estimating the number of limit cycles of autonomous systems on the plane},
     journal = {Differencialʹnye uravneni\^a},
     pages = {213--220},
     publisher = {mathdoc},
     volume = {42},
     number = {2},
     year = {2006},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2006_42_2_a8/}
}