@article{SM_1984_47_1_a1,
     author = {E. I. Pustyl'nik},
     title = {On~functions of a positive operator},
     journal = {Sbornik. Mathematics},
     pages = {27--42},
     year = {1984},
     volume = {47},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1984_47_1_a1/}
}