@article{DAN_1978_243_6_a7,
     author = {V. A. Il'in and I. Jo},
     title = {An estimate of the difference of the partial sums of expansions corresponding to two arbitrary nonnegative selfadjoint extensions of two operators of {Sturm--Liouville} type for an absolutely continuous function},
     journal = {Doklady Akademii Nauk},
     pages = {1381--1383},
     publisher = {mathdoc},
     volume = {243},
     number = {6},
     year = {1978},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1978_243_6_a7/}
}