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3. A. Miele (ed.), Theory of Optimum Aerodynamic Shapes, Academic Press, New York (1965).
4. A. N. Kraiko, Variational Problems of Gas Dynamics [in Russian], Nauka, Moscow (1979).
5. V. N. Monakhov, Free-Boundary Boundary-Value Problems for Elliptic Equations [in Russian], Nauka, Novosibirsk (1977).