@article{10_4153_CMB_2008_011_1,
     author = {Nakazato, Hiroshi and Bebiano, Nat\'alia and Provid\^encia, Jo\~ao da},
     title = {The {Numerical} {Range} of {2-Dimensional} {Krein} {Space} {Operators}},
     journal = {Canadian mathematical bulletin},
     pages = {86--99},
     year = {2008},
     volume = {51},
     number = {1},
     doi = {10.4153/CMB-2008-011-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2008-011-1/}
}