@article{DE_1986_22_9_a2,
     author = {\`E. I. Grudo},
     title = {Periodic solutions with incommensurable periods of periodic differential systems},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1499--1504},
     publisher = {mathdoc},
     volume = {22},
     number = {9},
     year = {1986},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1986_22_9_a2/}
}