1. G.S.S. Ávila and D.G. Costa, Decay of solutions of symmetric hyperbolic systems of partial differential equations (to appear in Rocky Mountain J. of Math.).
2. On partition of energy for uniformly propagative systems;Costa;J. Math. Anal. Appl.,1977
3. The Radon transform on Euclidean spaces…;Helgason;Acta Math.,1965
4. T. Ikebe, Scattering for uniformly propagative systems, Proc. Int. Conf. on Func. Anal, and Related Topics, Tokio (1969), pp. 225–230.
5. Scattering Theory;Lax,1967