Playing Around Resonance: An Invitation to the Search of Periodic Solutions for Second Order Ordinary Differential Equations (Softcover Reprint of thePaperback - Softcover Reprint of the Original 1st 2016, 29 June 2018

1.Preliminaries on Hilbert spaces.- 2.Operators in Hilbert spaces.- 3.The semilinear problem.- 4.The topological degree.- 5.Nonresonance and topological degree.- 6.Playing around resonance.- 7.The variational method.- 8.At resonance, again.- 9.Lusternik-Schnirelmann theory. 10.The Poincaré-Birkhoff theorem.- 11.A myriad of periodic solutions.