1. F. P. Vasil’ev, Solution Methods for Optimization Problems (Nauka, Moscow, 1981) [in Russian].
2. J.-L. Lions, Controle optimal de systemes gouvernes par des equations aux derivees partielles (Gauthier-Villars, Paris, 1968; Mir, Moscow, 1972).
3. K. A. Lur’e, Optimal Control in Problems of Mathematical Physics (Nauka, Moscow, 1975) [in Russian].
4. V. G. Litvinov, Optimization in Elliptic Boundary Problems with Applications in Mechanics (Nauka, Moscow, 1987) [in Russian].
5. U. E. Raitum, Optimal Control Problems for Elliptic Equations (Zinatne, Riga, 1989) [in Russian].