@article{GDZPPN002183935,
title = {Multiplicative properties of the numerical radius in operator theory.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {238},
year = {1969},
pages = {166-174},
zbl = {0176.43502},
url = {http://dml.mathdoc.fr/item/GDZPPN002183935}
}
Holbrook, John A R. Multiplicative properties of the numerical radius in operator theory.. Journal für die reine und angewandte Mathematik, Tome 238 (1969) pp. 166-174. http://gdmltest.u-ga.fr/item/GDZPPN002183935/