@article{AM2_1977__16_136672,
     author = {J.J. Koliha},
     title = {Convergence of an operator series.},
     journal = {Aequationes mathematicae},
     pages = {31--36},
     publisher = {mathdoc},
     volume = {16},
     year = {1977},
     zbl = {0376.47011},
     url = {http://geodesic.mathdoc.fr/item/AM2_1977__16_136672/}
}