2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/33825Contents. 1. Introduction. 2. Kinematics of a Material Medium: Material Representation. 3. Kinematics of a Material Medium: Convected Differentials. 4. Kinematics of a Perfect Elastic Medium. 5. Small Gravitational Perturbations of an Elastic Medium.14 pages TeX file of contrib. to proc. Gravitational Radiation, Les Houches 1982, ed N. Deruelle, T. Piran, 455-464 (North Holland, Amsterdam, 1983)General Relativity and Quantum Cosmologytext