@article{RCM_1979__13_181684,
     author = {Klaus Gero Kalb},
     title = {Characterization {Of} {Certain} {....-Self-Adjoint} {Operators} {By} {Means} {Of} {Their} {Exponential} {Function.}},
     journal = {Revista colombiana de matematicas},
     pages = {193--206},
     publisher = {mathdoc},
     volume = {13},
     year = {1979},
     zbl = {0438.47038},
     url = {http://geodesic.mathdoc.fr/item/RCM_1979__13_181684/}
}