1. Aizicovici, S., and Papageorgiou, N. S., Optimal Control and Relaxation of Systems Governed by Volterra Integral Equations, World Congress of Nonlinear Analysts, Edited by V. Lakshmikantham, Walter de Gruyter, Berlin, Germany, pp. 2617–2625, 1996.
2. Chryssoverghi, I., Contrôle Optimal Relaxé d'Equations Intégrales et aux Derivées Partielles, Doctoral Thesis, EPF, Lausanne, Switzerland, 1976.
3. Warga, J., Optimal Control of Differential and Functional Equations, Academic Press, New York, New York, 1972.
4. RoubiČek, T., Relaxation in Optimization Theory and Variational Calculus, Walter de Gruyter, Berlin, Germany, 1997.
5. Angell, T. S., On the Optimal Control of Systems Governed by Nonlinear Volterra Equations, Journal of Optimization Theory and Applications, Vol. 19, pp. 29–45, 1976.