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2. A. M. Samoilenko and N. A. Perestyuk, Differential Equations with Pulse Effects [in Russian], Vishcha Shkola, Kiev (1987).
3. V. A. Pliss, Integral Sets of Periodic Systems of Differential Equations [in Russian], Nauka, Moscow (1977).
4. S. I. Trofimchik, ?Sufficient conditions for the absence of ?throbbing? in pulse systems,? in: Differential Equations with a Parameter [in Russian], Inst. Mat. Akad. Nauk UKrSSR, Kiev (1989), pp. 133?139.
5. A. M. Samoilenko, N. A. Perestyuk, and M. U. Akhmetov, ?A comparison method for systems of differential equations with pulse effects? (Preprint, Akad. Nauk UkrSSR, Inst. Mat., No. 89.3), Kiev (1989).