1. Lions, J.L., Exact controllability, stabilization and perturbations for distributed systems, SIAM Rev., 1988, vol. 30, no. 1, pp. 1–68.
2. Zuazua, E., Exact controllability for the semilinear wave equation, J. Math. Pures Appl., 1990, vol. 69, pp. 1–31.
3. Triggiani, R., Exact boundary controllability in $$L_2(\Omega )\times H^{-1}(\Omega )$$ for the wave equation with Dirichlet control action at the boundary and related problems, Appl. Math. Optim., 1988, vol. 18, pp. 241–277.
4. Komornik, V.A., Exact Controllability and Stabilization. The Multiplier Method, Paris–Chichester: Wiley, 1994.
5. Butkovskii, A.G., Teoriya optimal’nogo upravleniya sistemami s raspredelennymi parametrami (Optimal Control Theory for Systems with Distributed Parameters), Moscow: Nauka, 1965.