@article{DE_1979_15_7_a2,
     author = {V. A. Il'in and I. Jo},
     title = {Estimation of the difference of partial sums of expansions corresponding to two arbitrary nonnegative selfadjoint extensions of two operators of {Sturm{\textendash}Liouville}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1175--1193},
     year = {1979},
     volume = {15},
     number = {7},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1979_15_7_a2/}
}