1. Ordinary Differential Equations;Arnold,1973
2. Periodic solutions of the differential equation ẍ + g(x) = p(t);Harvey;Contrib. Differential Equations,1962
3. Behaviour of solutions for certain types of nonlinear differential equations of the second order;Hayashi,1973
4. Differential Equations: Geometric Theory;Lefschetz,1962
5. Periodic solutions of nonlinear equations of Duffing type;Loud,1967