1. Nonlinear Two Point Boundary Value Problems;Bailey,1968
2. Stability Theory of Differential Equations;Bellman,1953
3. On some simple extensions of elliptic boundary value problems (Russian);Bitsadze;Dokl. Akad. Nauk. SSSR,1969
4. Über die Existenz der Lösungen von Radwertaufgaben min gewöhnlichen nichtlinearen Differentialgleichungen zweiter Ordnung;Epheser;Math. Z.,1955
5. Concerning the disconjugacy of second order singular linear differential equations (Russian);Gogiberidze;Differencial'nye Uravnenija,1974