@article{10_1017_S0017089500003244,
     author = {Au-Yeung, Yik-Hoi and Sing, Fuk-Yum},
     title = {A remark on the generalized numerical range of a normal matrix},
     journal = {Glasgow mathematical journal},
     pages = {179--180},
     year = {1977},
     volume = {18},
     number = {2},
     doi = {10.1017/S0017089500003244},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500003244/}
}