1. Theory of Ordinary Differential Equations;Coddington,1955
2. The Construction of Green's Functions for a Class of Hyperbolic Boundary Value Problems;Haws,1987
3. N. Iraniparast, Green-Riemann functions for a class of hyperbolic focal point problems, to appear.
4. On the Spectrum of a Self-Adjoint Problem for the Wave Equation;Kalmenov,1983
5. Positive Solutions of Operatir Equations;Krasnoselskii,1964