@article{AM2_1981__23_136910,
     author = {Dieter Lutz},
     title = {On bounded time-dependent perturbations of operator cosine functions.},
     journal = {Aequationes mathematicae},
     pages = {197--203},
     publisher = {mathdoc},
     volume = {23},
     year = {1981},
     zbl = {0512.34047},
     url = {http://geodesic.mathdoc.fr/item/AM2_1981__23_136910/}
}