@article{DE_1978_14_3_a3,
     author = {\`E. I. Grudo},
     title = {The complex centers and foci of a second order differential equation},
     journal = {Differencialʹnye uravneni\^a},
     pages = {425--434},
     publisher = {mathdoc},
     volume = {14},
     number = {3},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1978_14_3_a3/}
}