@article{MZ_1987__194_173812,
     author = {Ky Fan},
     title = {Sharpened {Forms} of an {Inequality} of {Von} {Neumann.}},
     journal = {Mathematische Zeitschrift},
     pages = {7--14},
     publisher = {mathdoc},
     volume = {194},
     year = {1987},
     zbl = {0631.47004},
     url = {http://geodesic.mathdoc.fr/item/MZ_1987__194_173812/}
}