@article{EJDE_2006__2006__a191,
     author = {Gao, Haiyin and Weng, Shiyou and Jiang, Daqing and Hou, Xuezhang},
     title = {On second order periodic boundary-value problems with upper and lower solutions in the reversed order},
     journal = {Electronic Journal of Differential Equations},
     publisher = {mathdoc},
     volume = {2006},
     year = {2006},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2006__2006__a191/}
}