@article{10_21136_CMJ_1960_100416,
     author = {Hsu, Leetsch C.},
     title = {An estimation for the first exponential formula in the theory of semigroups of linear operations},
     journal = {Czechoslovak Mathematical Journal},
     pages = {323--328},
     publisher = {mathdoc},
     volume = {10},
     number = {3},
     year = {1960},
     doi = {10.21136/CMJ.1960.100416},
     mrnumber = {0119102},
     zbl = {0096.32001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1960.100416/}
}