@article{DAN_1988_300_5_a7,
     author = {V. A. Sadovnichii and V. A. Lyubishkin},
     title = {Trace formulas and perturbation theory},
     journal = {Doklady Akademii Nauk},
     pages = {1064--1066},
     publisher = {mathdoc},
     volume = {300},
     number = {5},
     year = {1988},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1988_300_5_a7/}
}