@article{GDZPPN001264354, title = {Pertubation and comparison of cosine operator functions.}, journal = {Semigroup forum}, volume = {51}, year = {1995}, pages = {225-246}, zbl = {0828.47037}, url = {http://dml.mathdoc.fr/item/GDZPPN001264354} }
Piskarev, S.; Shaw, S.YX. Pertubation and comparison of cosine operator functions.. Semigroup forum, Tome 51 (1995) pp. 225-246. http://gdmltest.u-ga.fr/item/GDZPPN001264354/