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2008.
A spectrality condition for infinitesimal generators of cosine operator functions
. We will give a necessary and sufficient condition for the infinitesimal generator of a strongly continuous cosine operator function C ( t ), such that (cid:107) C ( t ) (cid:107) ≤ 1 for all t ∈ R on a reflexive, strictly convex (complex) Banach space with a Gˆateaux differentiable norm to be a spectral scalar type operator with the spectral family of hermitian bounded linear projectors.