@article{EXMATH_1987_1987_1_a21,
     author = {Acosta, Mar{\'\i}a D. and Pay\'a Albert, Rafael},
     title = {Operadores que alcanzan el radio num\'erico.},
     journal = {Extracta mathematicae},
     pages = {74-76},
     publisher = {mathdoc},
     volume = {2},
     number = {2},
     year = {1987},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EXMATH_1987_1987_1_a21/}
}