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@article{DE_1981_17_8_a10, author = {D. Safarov}, title = {Periodic solutions of first-order elliptic systems}, journal = {Differencialʹnye uravneni\^a}, pages = {1468--1477}, publisher = {mathdoc}, volume = {17}, number = {8}, year = {1981}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1981_17_8_a10/} }
D. Safarov. Periodic solutions of first-order elliptic systems. Differencialʹnye uravneniâ, Tome 17 (1981) no. 8, pp. 1468-1477. http://geodesic.mathdoc.fr/item/DE_1981_17_8_a10/