@article{DE_1979_15_6_a4,
     author = {S. Yu. Pilyugin},
     title = {Periodic trajectories and the structure of phase diagrams},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1000--1006},
     publisher = {mathdoc},
     volume = {15},
     number = {6},
     year = {1979},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1979_15_6_a4/}
}