@article{DAN_1981_257_5_a0,
     author = {Yu. Sh. Abramov},
     title = {Numerical ranges, zones, and spectra of families of selfadjoint operators},
     journal = {Doklady Akademii Nauk},
     pages = {1033--1037},
     publisher = {mathdoc},
     volume = {257},
     number = {5},
     year = {1981},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1981_257_5_a0/}
}