1. On nonlinear oscillation for a second order delay equation;Gollwitzer;J. Math. Anal. Appl.,1969
2. On the oscillation and nonoscillation of solutions of nonlinear differential systems;Iziumova;Differencial'nye Uravnenija,1976
3. Nonlinear oscillation of second order differential equations with retarded argument;Kusano;Ann. Mat. Pura Appl.,1975
4. Some problems of the theory of almost periodic functions I;Levitan;Uspehi Mat. Nauk.,1947
5. On the oscillation of solutions of a system of nonlinear differential equations;Mirzov;Differencial'nye Uravnenija,1973