@article{10_21136_CPM_1968_117636,
     author = {Sova, Miroslav},
     title = {Semigroups and cosine function of normal operators in {Hilbert} spaces},
     journal = {\v{C}asopis pro p\v{e}stov\'an{\'\i} matematiky},
     pages = {437--458},
     publisher = {mathdoc},
     volume = {093},
     number = {4},
     year = {1968},
     doi = {10.21136/CPM.1968.117636},
     mrnumber = {0250121},
     zbl = {0172.40606},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CPM.1968.117636/}
}