@article{GDZPPN00203350X, title = {On bounded time-dependent perturbations of operator cosine functions.}, journal = {Aequationes mathematicae}, volume = {22}, year = {1981}, pages = {197-203}, zbl = {0512.34047}, url = {http://dml.mathdoc.fr/item/GDZPPN00203350X} }
Lutz, Dieter. On bounded time-dependent perturbations of operator cosine functions.. Aequationes mathematicae, Tome 22 (1981) pp. 197-203. http://gdmltest.u-ga.fr/item/GDZPPN00203350X/