@article{TIMB_2009_17_1_a4,
     author = {P. P. Zabreiko and O. Y. Kushel},
     title = {Gantmakher--Krein theorem for $2$-completely nonnegative operators in ideal spaces},
     journal = {Trudy Instituta matematiki},
     pages = {51--60},
     publisher = {mathdoc},
     volume = {17},
     number = {1},
     year = {2009},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TIMB_2009_17_1_a4/}
}