@article{DE_1998_34_3_a15,
     author = {Yu. G. Bulychev},
     title = {A general theory of approximate methods for constructing parametrized solutions of linear differential equations},
     journal = {Differencialʹnye uravneni\^a},
     pages = {395--402},
     publisher = {mathdoc},
     volume = {34},
     number = {3},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1998_34_3_a15/}
}