@article{ZNSL_1982_107_a12,
     author = {Yu. Sh. Abramov},
     title = {Duality in spectral optimization and numerical ranges of a~family of self-adjoint operators},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {189--192},
     year = {1982},
     volume = {107},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1982_107_a12/}
}