1. A simple alternative problem for finding periodic solution of second order ordinary differential systems;Bebernes,1974
2. Inequalities;Beckenbach,1961
3. Periodic solution of certain second order nonlinear differential equations;Chang;J. Math. Anal. Appl.,1975
4. Fixed Points and Topological Degree in Nonlinear Analysis;Cronin,1964
5. Some new criteria for the existence of periodic solutions of a certain second order differential equation;Ezeilo;Atti Accad. Naz. Lincei Rend. Cl. Sci. Fis. Mat. Natur.,1974