@article{DE_2005_41_8_a14,
     author = {Yu. S. Kolesov},
     title = {Proof of {Levin's} {Half-Period} {Theorem}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1125--1127},
     publisher = {mathdoc},
     volume = {41},
     number = {8},
     year = {2005},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2005_41_8_a14/}
}