... Zheng and Q. Zhang, Existence and multiplicity of solutions of second-order difference boundary value problems,” Acta Applicandae Mathematicae, vol. 110, no. 1, pp. 131–152, 2010.6 X. Cai and ... ProblemsVolume 2011, Article ID 172818, 19 pagesdoi:10.1155/2011/172818 Research Article Existence of Positive, Negative, and Sign-Changing Solutions to Discrete Boundary Value ProblemsBo Zheng,1Huafeng ... positive and write u>0 if for all n ∈1,T,un ≥ 0, and {n ∈ 1,T: un > 0}/ ∅, and similarly,2 Boundary Value Problemsu is negative u<0 if for all n ∈1,T,un ≤ 0, and {n...