1. Lectures on Functional Equations and their Applications;Aczél,1966
2. Functional Equations: History, Applications and Theory;Aczél,1984
3. Functional Equations Containing Several Variables;Aczél,1989
4. Geometrical Methods in the Theory of Ordinary Differential Equations;Arnold,1983
5. Methods of Nonlinear Analysis;Bellman,1973