1. Dynamic Equations on Time Scales. An Introduction with Applications;Bohner,2001
2. Nonlinear Problems in Abstract Cones;Guo,1988
3. Bounds for positive solutions for a focal boundary value problem;Atici;Comput. Math. Appl.,1998
4. Boundary Value Problems for Higher Order Differential Equations;Agarwal,1986
5. On the existence of positive solutions of ordinary differential equations;Erbe,1994