1. Clarke, F. H.: Nonsmooth Analysis and Optimization. J. Wiley 1983.
2. Taubert, K.: Converging multistep methods for initial value problems involving multivalued maps. Computing27, 123 (1981).
3. Pshenichny, B. N.: Convex Analysis and Optimization. Moscow: Nauka 1980 (russian).
4. Dontchev, A. L.: Equivalent perturbations and approximations in optimal control. C. R. Bulg. Acad. Sci.39, 27 (1986).
5. Mordukhovič, B. S.: A contribution to the theory of finite difference approximations to optimal control problems. Doklady AN BSSR30, 1064 (1986) (russian).