1. Hestenes, M. R., andGuinn, T.,An Embedding Theorem for Differential Equations, Journal of Optimization Theory and Applications, Vol. 2, No. 2, 1968.
2. Hestenes, M. R.,Calculus of Variations and Optimal Control Theory, John Wiley and Sons, New York, New York, 1966.
3. Bakke, V. L.,A Maximum Principle for Optimal Control Problems with Integral Constraints, Journal of Optimization Theory and Applications, Vol. 13, No. 1, 1974.
4. Tricomi, F. G.,Integral Equations, John Wiley and Sons (Interscience Publishers), New York, New York, 1957.
5. Sato, T., Sur l'Équation Intégrale Non Linéaire de Volterra, Compositio Mathematica, Vol. 11, pp. 271?290, 1953.