1. Bardos, C., Lebeau G., Rauch, J., Un example d’utilisation des notions de propagation pour le contrôle et la stabilisation des problèmes hyperboliques, Rend. Sem. Mat. Univ. Pol. Torino, 1988, Spec. Issue (1989): 11–31.
2. Lagnese, J., Control of wave processes with distributed controls supported on a subregion, SIAM Journal of Control and Optimization, 1983, 21: 68–85.
3. Liu, K., Locally distributed control and damping for the conservative systems, SIAM Journal of Control and Optimization, 1997, 35: 1574–1590.
4. Wu, H., Shen, L. L. Yu, Y. L., Introduction to Riemannian Geometry (in Chinese), Beijing: Peking University Press, 1989.
5. Yao, P. F., On the observability inequality for exact controllability of wave equations with variable coefficients, SIAM Journal of Control and Optimization, 1999, 37: 1568–1599.