@article{10_4064_sm_54_2_143_147,
     author = {V. Pellegrini},
     title = {Numerical range preserving operators on a {Banach} algebra},
     journal = {Studia Mathematica},
     pages = {143--147},
     publisher = {mathdoc},
     volume = {54},
     number = {2},
     year = {1975},
     doi = {10.4064/sm-54-2-143-147},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-54-2-143-147/}
}