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@article{DE_1976_12_3_a0, author = {N. P. Erugin}, title = {Theory of moving singular points of second order {equations.~I}}, journal = {Differencialʹnye uravneni\^a}, pages = {387--416}, publisher = {mathdoc}, volume = {12}, number = {3}, year = {1976}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DE_1976_12_3_a0/} }
N. P. Erugin. Theory of moving singular points of second order equations.~I. Differencialʹnye uravneniâ, Tome 12 (1976) no. 3, pp. 387-416. http://geodesic.mathdoc.fr/item/DE_1976_12_3_a0/