RT Journal T1 Existence of positive solutions for periodic boundary conditions of singular second-order damped difference equations A1 SU Xiao-xiao PB JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) FD YR 2019 JF JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) JO JOURNAL OF SHANDONG UNIVERSITY(NATURAL SCIENCE) VO 54 IS 12 SP 38 DO 10.6040/j.issn.1671-9352.0.2019.461 K1 difference equation;positive solution;singular;Greens function;nonlinear alternative of Leray-Schauder LK {http://lxbwk.njournal.sdu.edu.cn/EN/article/article_3188.shtml}