1. Periodic boundary value problems for systems of second order differential equations;Bebernes;J. Differential Equations,1973
2. An existence theorem for periodic boundary value problems for systems of second order differential equations;Bebernes;Arch. Math.,1972
3. S. R. Bernfeld, G. S. Ladde, and V. Lakshmikantham, Existence of solutions of two point boundary value problems for nonlinear systems, to appear.
4. Periodic solutions of hereditary differential systems;Gustafson;J. Differential Equations,1973
5. On boundary value problems for systems of ordinary nonlinear second order differential equations;Hartman;Trans. Amer. Math. Soc.,1960