@article{DE_1999_35_3_a10,
     author = {B. I. Bandyrskii and V. L. Makarov and O. L. Ukhanev},
     title = {Sufficient conditions for the convergence of nonclassical asymptotic expansions for the {Sturm--Liouville} problem with periodic conditions},
     journal = {Differencialʹnye uravneni\^a},
     pages = {367--378},
     publisher = {mathdoc},
     volume = {35},
     number = {3},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_3_a10/}
}