@article{DE_1977_13_7_a12,
     author = {V. A. Sadovnichy and V. V. Dubrovskii},
     title = {An abstract theorem of perturbation theory, regularized trace formulas, and the zeta function of operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1264--1271},
     publisher = {mathdoc},
     volume = {13},
     number = {7},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_7_a12/}
}