In this paper we show that from an estimate of the form , we can conclude that C(t) equals cos(at)I. Here is a strongly continuous cosine family on a Banach space.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-sm8218-12-2015, author = {Felix L. Schwenninger and Hans Zwart}, title = {Less than one implies zero}, journal = {Studia Mathematica}, volume = {231}, year = {2015}, pages = {181-188}, zbl = {1337.47063}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm8218-12-2015} }
Felix L. Schwenninger; Hans Zwart. Less than one implies zero. Studia Mathematica, Tome 231 (2015) pp. 181-188. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm8218-12-2015/