We investigate the periodic solutions of second-order difference problem with potential indefinite in sign. We consider the compactness condition of variational functional and local linking at 0 by introducing new number . By using Morse theory, we obtain some new results concerning the existence of nontrivial periodic solution.
"Periodic Solutions of Second-Order Difference Problem with Potential Indefinite in Sign." Abstr. Appl. Anal. 2013 (SI55) 1 - 8, 2013. https://doi.org/10.1155/2013/517036