@article{EXMATH_2001_2001_1_a14,
     author = {Barraa, Mohamed and Boumazgour, Mohamed},
     title = {Norma de una derivaci\'on y operadores hiponormales.},
     journal = {Extracta mathematicae},
     pages = {229-233},
     publisher = {mathdoc},
     volume = {16},
     number = {2},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EXMATH_2001_2001_1_a14/}
}