1. Toma, C.: An extension of the notion of observability at filtering and sampling devices. In: Proceedings of the International Symposium on Signals, Circuits and Systems Iasi SCS 2001, Romania, pp. 233–236 (2001)
2. Lecture Notes in Computer Science;G. Toma,2005
3. Dzurina, J.: Oscillation of second order differential equations with advanced argument. Math. Slovaca 45(3), 263–268 (1995)
4. Zhang, Z., Ping, B., Dong, W.: Oscillation of unstable type second order nonlinear difference equation. Korean J. Computer and Appl. Math. 9(1), 87–99 (2002)
5. Lecture Notes in Computer Science;F. Doboga,2005