... Difference EquationsVolume 2009, Article ID 737461, 14 pagesdoi:10.1155/2009/737461 Research Article Necessary and Sufficient Conditions for the Existence of Positive Solution for Singular Boundary Value ... standardtopology on R and say t is right scattered, left scattered, right dense and left dense if σt >t, ρt <t,σtt, and ρtt, respectively. Finally, we introduce the sets Tk and ... Nonoscillation and Oscillation: Theory for Functional DifferentialEquations, vol. 267 of Monographs and Textbooks in Pure and Applied Mathematics, Marcel Dekker, NewYork, NY, USA, 2004.10 M. Bohner and...