@article{MT_1987_9_a14,
     author = {V. V. Ivanov},
     title = {Uniformly summable semigroups of operators. {II.~Perturbation} of semigroups},
     journal = {Matemati\v{c}eskie trudy},
     pages = {159--182},
     publisher = {mathdoc},
     volume = {9},
     year = {1987},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MT_1987_9_a14/}
}