1. Yakubovich, V.A., Solution of some Matrix Inequalities Encountered in the Automatic Control Theory, Dokl. Akad. Nauk SSSR, 1962, vol. 143, no. 6, pp. 1304–1307.
2. Kalman, R.E., Lyapunov Functions for the Problem of Lur’e in Automatic Control, Proc. USA National Acad. Sci., 1963, vol. 49, no. 1, pp. 201–205.
3. Gantmakher, F.R. and Yakubovich, V.A., Absolute Stability of the Nonlinear Controllable Systems, Tr. II Vsesoyuz. s“ezda po teoreticheskoi i prikladnoi mekhanike (Proc. II All-Union Conf. Theoretical Applied Mechanics, 1964), Moscow: Nauka, 1965.
4. Popov, V.M., Hyperstability and Optimality of Automatic Systems with Several Control Functions, Rev. Roumaine Sci. Tech., 1964, vol. 9, no. 4, pp. 629–890.
5. Lefschetz, S., Stability of Nonlinear Control Systems, New York: Academic, 1965.