@article{DE_1999_35_4_a7,
     author = {V. A. Sadovnichii and A. Yu. Popov},
     title = {An estimate for the best approximation of solutions of the {Sturm--Liouville} equation with an analytic potential by partial sums of asymptotic series},
     journal = {Differencialʹnye uravneni\^a},
     pages = {498--506},
     publisher = {mathdoc},
     volume = {35},
     number = {4},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_4_a7/}
}