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This book provides an up-to-date description of the methods needed to face the existence of solutions to some nonlinear boundary value problems. All important and interesting aspects of the theory of periodic solutions of ordinary differential equations related to the physical and mathematical question of resonance are treated. The author has chosen as a model example the periodic problem for a second order scalar differential equation. In a paedagogical style the author takes the reader step by step from the basics to the most advanced existence results in the field.

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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.

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"Fonda´s Playing Around Resonance focuses on the material needed to develop research in ´the existence of solutions´ to a type of nonlinear boundary value problem. In particular, he concentrates on providing the theory to research periodic solutions to second order ordinary differential equations. ... it is truly geared more toward graduate students. Summing Up: Recommended. Graduate students, researchers, and faculty." (S. L. Sullivan, Choice, Vol. 54 (11), July, 2017)

"This is an excellent book, well organized and full of well-explained results and techniques on the subject. The proofs of the theorems are rigorous and well written, the arguments are presented in a clear and pleasurable way. The final section of each chapter ... provides information useful to a better understanding of the history of the results contained in the book. ... used as a textbook in an advanced course dealing with periodic solutions for second-order ordinary differential equations." (Addolorata Salvatore, Mathematical Reviews, 2017)

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