%0 Journal Article
%A Jan Niechwiej
%T Cosine Functions of Unbounded Operators and Second Order Differential Equations
%J Mathematica balkanica
%D 1990
%P 329
%V 4
%N 3-4
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MABA_1990_4_3-4_a10/
%F MABA_1990_4_3-4_a10