@article{SM_1968_6_3_a1,
     author = {Yu. L. Shmul'yan},
     title = {On operator balls and linear-fractional transformations with operator coefficients},
     journal = {Sbornik. Mathematics},
     pages = {309--326},
     publisher = {mathdoc},
     volume = {6},
     number = {3},
     year = {1968},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1968_6_3_a1/}
}