1. A. G. Butkovsky, A. Ya. Lerner, Automatica and Telemechanic, 21 (6), 682–691 (1960).
2. A. G. Butkovsky, American Elsevier Publishing (1969)
3. R. K. Tagiyev, Automation and Remore Control, 73 (7), 40–54 (2012)
4. A. D. Iskenderov, G. Ya. Yagubov, Soviet Math. Dokl.(English Trans.). AMS 38 (1989)
5. A. D. Iskenderov, G. Ya. Yagubov, Automatica and Telemechanic 12, 27–38 (1989).