1. Andronov, A. A., Vitt, A. A., and Haikin, S. Z. (1959).Oscillation Theory, Fizmatgiz, Moscow (in Russian).
2. Bainov, D. D., and Milusheva, S. D. (1981). Investigation of partially-multiplicative averaging for a class of functional differential equations with variable structure and impulses,Tsukuba Journal of Mathematics,9(1), 1?19.
3. Dishliev, A. B., and Bainov, D. D. (1987). Continuous dependence on the initial condition of the solution of a system of differential equations with variable structure and with impulses,Publications RIMS, Kyoto University,23(6), 923?936.
4. Emel'yanov, S. V. (1970).Theory of Systems with Variable Structure, Nauka, Moscow (in Russian).
5. Halanay, A., and Veksler, D. (1974).Qualitative Theory of Impulse Systems, Mir, Moscow (in Russian).