@article{10_1017_S0017089500006455,
     author = {Tam, Bit-Shun},
     title = {A {Simple} proof of the {Goldberg{\textendash}Straus} theorem on numerical radii},
     journal = {Glasgow mathematical journal},
     pages = {139--141},
     year = {1986},
     volume = {28},
     number = {2},
     doi = {10.1017/S0017089500006455},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500006455/}
}