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@article{DAN_1969_184_2_a9, author = {E. L. Tonkov}, title = {The second order periodic equation}, journal = {Doklady Akademii Nauk}, pages = {296--299}, publisher = {mathdoc}, volume = {184}, number = {2}, year = {1969}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DAN_1969_184_2_a9/} }
E. L. Tonkov. The second order periodic equation. Doklady Akademii Nauk, Tome 184 (1969) no. 2, pp. 296-299. http://geodesic.mathdoc.fr/item/DAN_1969_184_2_a9/