1. A. Matveev and V. Jakubovich, Optimal control for a system with distributed parameters. J. Sib. Math. 19 (1978), 5, 1109–1140.
2. D. Tiba, Optimality conditions for nonlinear distributed control problems. Proc. 22 IEEE Conf. N.Y. Dec. Contr., 1983, 1251–1252.
3. A.V. Fursikov, Optimal Control of Distributed Systems, Theory and Applications. Providence, Amer. Math. Soc., 1999.
4. D. Tiba, Optimal control for second-order semilinear hyperbolic equations. Contr. Theory Adv. Techn. 3 (1987), 1, 33–46.
5. V. Sumin, About relaxation of optimization problems for functional equations in spaces of essential bounded functions. Vestnik Nizhegorod. Univ. 1998, 1, 126–133.