Permanence and periodic solution of predator-prey system with holling type functional response and impulses. Wang, Weibing, Shen, Jianhua, Nieto, Juan J. (2007) Discrete Dynamics in Nature and Society
Permanence and stability of an age-structured prey-predator system with delays. Cai, Liming, Li, Xuezhi, Song, Xinyu, Yu, Jingyuan (2007) Discrete Dynamics in Nature and Society
Positive solutions of Volterra integro-differential equations. Wu, Yumei (1995) Acta Mathematica Universitatis Comenianae. New Series