@article{GDZPPN001257595,
title = {Semigroups of operators and second-order Cauchy problems.},
journal = {Semigroup forum},
volume = {31},
year = {1985},
pages = {297-304},
zbl = {0557.47028},
url = {http://dml.mathdoc.fr/item/GDZPPN001257595}
}
Dorroh, J.R. Semigroups of operators and second-order Cauchy problems.. Semigroup forum, Tome 31 (1985) pp. 297-304. http://gdmltest.u-ga.fr/item/GDZPPN001257595/