@article{10_1017_S0017089500007989,
     author = {Grobler, J. J. and Raubenheimer, H.},
     title = {Spectral properties of elements in different {Banach} algebras},
     journal = {Glasgow mathematical journal},
     pages = {11--20},
     year = {1991},
     volume = {33},
     number = {1},
     doi = {10.1017/S0017089500007989},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500007989/}
}