1. Alternative problems for non-linear functional equations;Bancroft;J. Differential Equations,1968
2. Functional analysis and Galerkin's method;Cesari;Michigan J. Math.,1964
3. Periodic solutions of nonlinear systems of differential equations;Hale;Riv. Mat. Univ. Parma,1954
4. J. Henrard, Lyapunov's center theorem for resonant equilibrium, to appear, J. Differential Equations.
5. Periodic orbits near L4 for mass ratios near the critical mass ratio of Routh;Meyer;Celestial Mechanics,1971