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@article{DE_1969_5_3_a17, author = {G. S. Rychkov}, title = {The uniqueness of the limit cycle of the system $\dot y=-g(x)$, $\dot x=-f(x)$}, journal = {Differencialʹnye uravneni\^a}, pages = {563--564}, publisher = {mathdoc}, volume = {5}, number = {3}, year = {1969}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1969_5_3_a17/} }
G. S. Rychkov. The uniqueness of the limit cycle of the system $\dot y=-g(x)$, $\dot x=-f(x)$. Differencialʹnye uravneniâ, Tome 5 (1969) no. 3, pp. 563-564. http://geodesic.mathdoc.fr/item/DE_1969_5_3_a17/