1. V. N. Danilov, in Ill-Posed Problems (Nauka, Moscow, 1974), Ch. 1, p. 31 [in Russian].
2. V. N. Danilov, in Ill-Posed Problems (Nauka, Moscow, 1974), Ch. 1, p. 38 [in Russian].
3. V. N. Danilov, in Ill-Posed Problems (Nauka, Moscow, 1974), Ch. 2, p. 61 [in Russian].
4. V. N. Danilov, in Ill-Posed Problems (Nauka, Moscow, 1974), Ch. 2, p. 67 [in Russian].
5. V. N. Danilov, Radiotekh. Elektron. (Moscow) 22, 2353 (1977).