1. Boltyanskii, V. G., R. V. Gamkrelize & L. S. Pontryagin: The theory of optimal processes. Izvestia Akad. Nauk SSSR, Ser. Mat. 24, No. 1 (1960) [in Russian].
2. Liapounov, A.: Sur les fonctions-vecteurs compl�tement additives. Bull. Acad. Sci. U.R.S.S. 4 (1940) [in Russian with a French r�sum�].
3. Halkin, H.: The Principle of Optimal Evolution, in Contributions to the Theory of Differential Equations, vol. III. New York: MacMillan 1962.