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3. V. V. Kastron, A. M. Kats, G. Ya. Dubur, and G. O. Silenietse, USSR Inventor's Certificate No. 568641 (1976);
4. Byull. Izobr., No. 30, 55 (1977).
5. A. M. Kats, V. V. Kastron, and G. Ya. Dubur, Khim. Geterotsikl. Soedin., No. 4, 555 (1977).