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@article{DAN_1964_157_2_a12, author = {Karl-Peter Hadeler}, title = {Estimates for the spectrum of normal operators}, journal = {Doklady Akademii Nauk}, pages = {284--287}, publisher = {mathdoc}, volume = {157}, number = {2}, year = {1964}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/DAN_1964_157_2_a12/} }
Karl-Peter Hadeler. Estimates for the spectrum of normal operators. Doklady Akademii Nauk, Tome 157 (1964) no. 2, pp. 284-287. http://geodesic.mathdoc.fr/item/DAN_1964_157_2_a12/