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2. N. G. Basov, P. A. Bazhulin, O. N. Krokhin, A. N. Oraevsky, and I. I. Sobel’man, Technical Report No. F-1470 [in Russian], P. N. Lebedev Physical Institute, Moscow (1965).
3. A. N. Tikhonov, N. G. Basov, A. A. Samarsky, O. N. Krokhin, N. I. Kozlov, and A. A. Filyukov, Joint Technical Report of the P. N. Lebedev Physical Institute, the Department of Applied Mathematics of the V. A. Steklov Mathematical Institute, and the Institute of Physics of Atmosphere No. F-1427 [in Russian], P. N. Lebedev Physical Institute, Moscow (1964).
4. Ya. B. Zel’dovich, Private communication by S. B. Kormer (1963).
5. S. B. Kormer and G. A. Kirillov, Technical Report No. 3859 [in Russian], Research Institute of Experimental Physics, Arzamas-16 (1963).