@article{DE_1975_11_10_a5,
     author = {E. K. Ershov},
     title = {Dependence on a parameter of the rotation number of a differential equation defined on the torus},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1774--1779},
     publisher = {mathdoc},
     volume = {11},
     number = {10},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1975_11_10_a5/}
}