@article{MAN_1979__246_163343,
     author = {Frank Hansen},
     title = {An {Operator} {Inequality.}},
     journal = {Mathematische Annalen},
     pages = {249--250},
     year = {1979},
     volume = {246},
     zbl = {0407.47012},
     url = {http://geodesic.mathdoc.fr/item/MAN_1979__246_163343/}
}