1. O. A. Ladyzhenskaya, Boundary-Value Problems of Mathematical Physics [in Russian], Nauka, Moscow (1973).
2. J.-L. Lions, Optimal Control of Systems Described by Partial Differential Equations [Russian translation], Mir, Moscow (1972).
3. V. P. Mikhailov, Partial Differential Equations [in Russian], Nauka, Moscow (1983).
4. F. Riesz and B. Sz.-Nagy, Lectures in Functional Analysis [Russian translation], Mir, Moscow (1979).