1. Soluzioni quasi-periodiche, o limitate, di sistemi differenziali nonlinear quasi-periodiche, o limitati;Amerio;Ann. Mat. Pura Appl.,1955
2. Periodic solutions of singularly perturbed equations;Flatto;J. Math. and Mech.,1955
3. Perturbations of nonlinear systems;Lillo;Acta Math.,1960
4. On the asymptotic stability of the solutions of systems of differential equations;Lyashchenko;Doklady Akad. Nauk. SSSR,1954
5. Global stability criteria for differential systems;Markus,1960