1. N. P. Bhatia andO. Hájek, Semi-dynamical systems (to appear).
2. O. Hájek, Structure of dynamical systems.Comment. Math. Univ. Carolinae 6 (1965), 53–72; correction,ibid. 6 (1965).
3. O. Hájek,Dynamical Systems in the Plane. Academic Press (in print).
4. G. R. Sell, Nonautonomous differential equations and topological dynamics. I.Trans. Amer. Math. Soc. 127 (1967), 241–262.
5. T. Ura, Prolongations of characteristics and the stability problem (in Japanese).Sûgaku 9 (1958), 137;ibid. 9 (1958), 218.