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Differential Equations (Springer, New York–Berlin–Heidelberg-Tokyo, 1986; Mir,
Moscow, 1989).
4. A. M. Vinogradov, Symmetries and
Conservation Laws of Equations of Mathematical Physics (Faktorial, Moscow, 1997)
[in Russian].
5. A. F. Sidorov, V. P. Shapeev, and N. N. Yanenko, The differential Constraint Method and Application in Gas
Dynamics (Nauka, Novosibirsk, 1984) [in Russian].