@article{10_21136_CPM_1984_108502,
     author = {Pt\'ak, Vlastimil},
     title = {A maximum problem for operators},
     journal = {\v{C}asopis pro p\v{e}stov\'an{\'\i} matematiky},
     pages = {168--193},
     publisher = {mathdoc},
     volume = {109},
     number = {2},
     year = {1984},
     doi = {10.21136/CPM.1984.108502},
     mrnumber = {744874},
     zbl = {0547.47004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CPM.1984.108502/}
}