1. USSR Patent No. 614795, Otkrytiya, No. 28 (1978).
2. USSR Patent No. 623359, ibid., No. 33 (1981).
3. USSR Patent No. 647940, ibid., No. 42 (1979).
4. USSR Patent No. 677298, ibid., No. 33 (1981).
5. Czechoslovakia Patent No. 159044, Ref. Zh. Khim., No. 20 0 91 P (1976).