1. Theory of Ordinary Differential Equations;Coddington,1955
2. Ordinary Differential Equations;Hale,1969
3. Periodic solutions of differential equation ẍ + g(x) = p(t);Harvey;Contributions to Differential Equations,1963
4. Boundedness and convergence of solutions of ẍ + c}x + g(x) = e(t);Loud;Duke Math. J.,1957
5. Topology From the Differentiable Viewpoint;Milnor,1966