“Necessary Conditions for Existence of Positive Solutions of Second Order Linear Difference Equations and Sufficient Conditions for Oscillation of Solutions”. Neliniini Kolyvannya 12, no. 2 (June 29, 2009): 180–194. Accessed January 21, 2026. https://twinhead.imath.kiev.ua/index.php/nosc/article/view/519.