@article{MMO_1971_25_a4,
     author = {A. D. Bruno},
     title = {Analytic form of differential {equations.~I,~II}},
     journal = {Trudy Moskovskogo matemati\v{c}eskogo ob\^{s}estva},
     pages = {119--262},
     publisher = {mathdoc},
     volume = {25},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MMO_1971_25_a4/}
}