On second order periodic boundary-value problems with upper and lower solutions in the reversed order. Gao, Haiyin; Weng, Shiyou; Jiang, Daqing; Hou, Xuezhang — 2006 Electronic Journal of Differential Equations (EJDE) [electronic only]
Upper and lower solutions for a second-order three-point singular boundary-value problem. Zhang, Qiumei; Jiang, Daqing; Weng, Shiyou; Gao, Haiyin — 2009 Electronic Journal of Differential Equations (EJDE) [electronic only]