1. Albarakati, W.A., Lloyd, N.G., Pearson, J.M.: Transformation to Liénard form. EJDE 2000(76), 1–11 (2000)
2. Amerio, L.: Soluzioni quasi-periodiche, o limitate, di sistemi differenziali non lineari quasi-periodici, o limitati Annali di Matematica Pura ed Applicata 39, 97–119 (1955)
3. Amor, H.B., Glade, N., Lobos, C., Demongeot, J.: The isochronal fibration: characterization and implication in biology. Acta Biotheor. 58(2), 121–142 (2010)
4. Andronov, A.A. et al.: Theory of Oscillators Dover, New York (1989)
5. Arnold, V.: Chapites supplémentaires de la Théorie des équations différentielles ordinaires. Editions MIR, Moscou (1978)