1. Yu. D. Shmyglevskii, Some Variational Problems of Gas Dynamics [in Russian], Vychisl. Tsentr. Akad. Nauk SSSR (1963).
2. A. N. Kraiko, Prikl. Mat. Mekh.,30, No. 2 (1966).
3. V. Ya. Neiland and V. V. Sychev, Uch. Zap. Tsentr. Aerogidrodin. Inst.,1, No. 1 (1970).
4. V. Ya. Neiland and G. I. Taganov, Inzh. Zh.,3, No. 2 (1963).
5. Yu. M. Davydov, Zh. Vychisl. Mat. Mat. Fiz., No. 2 (1975).