@article{RM_1965_20_6_a13,
     author = {P. P. Zabreiko and M. A. Krasnosel'skii and E. I. Pustyl'nik},
     title = {A~problem on fractional powers of operators},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     publisher = {mathdoc},
     volume = {20},
     number = {6},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1965_20_6_a13/}
}