@article{DE_1977_13_8_a28, author = {V. V. Amel'kin}, title = {Letter to the editors: {``On} the question of the isochrony of the center of two-dimensional analytic differential systems'' {(Differencial'nye} {Uravnenija} \textbf{13} (1977), no.~6, 971--980)}, journal = {Differencialʹnye uravneni\^a}, pages = {1537}, publisher = {mathdoc}, volume = {13}, number = {8}, year = {1977}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1977_13_8_a28/} }